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**DONOTDELETE** 05-21-2005 09:18 AM

vacuum advance question
 
Hi all, been a long time. My 1979 CJ-7 has been revived with a engine transplant, and now we're in the long slow road to recovery. Now I'm stumped, and I am in need of some sage advice. Here's my problem:

almost two years ago, my CJ threw a rod through the cylinder wall and so I had to get a new 258. My money situation being what it was (still is), I bought a used 258 from a Jeep junkyard (1975 cj-5) and put it in there. I put my MC2100 back on it, along with a new-to-me Chevy HEI upgrade with all new guts except the vacuum advance (which I had checked with my patented precision suck-on-the-hose test). After much drama with other systems, I got it to start and stay running. However, it's straining to go 40 mph.

So I bought a vacuum pump and ran a few tests:

- tested the vacuum with the engine at idle using my timing light. The timing appeared to advance way too fast when I would increase RPMs (as in it idled at about 3 BTDC, and jumps quickly past 21 BTDC and off the charts).

- tested the vacuum advance diaphragm with the dist. cap off using the vacuum pump. It started moving a little before 5 in-Hg, and reached maximum movement at about 18. I tested a new diaphragm, and it maxed about 15.

-Tested the vacuum off the MC2100 at varied RPMs. I didn't have a tach hooked up, but I can tell you it sucked past 18 in-Hg at light throttle (approx 1500 RPM, but it's just a rough guess).

I figured that there was too much vacuum for it to go directly to the distributor, and the vacuum diagrams I found when I searched this site and looked here looked like a road map to parts I didn't know existed. I tried porting out of the top of the carb, under the air cleaner, but that's just open air behind the air filter, so no vacuum. I also tried porting it through the valve cover emission stuff, but that also is no vacuum.

I need to reduce the amount of vacuum my mc2100 is providing. I am using the ported vacuum at the base of the carb on the engine side (right under the choke assembly), and that's the only vacuum port I can find. It varies (a lot) under load, so I know it's not manifold vacuum. Anyone got any advice? Thanks for lookin'.

RRich 05-21-2005 09:58 AM

Re: vacuum advance question
 
Nearly impossible to change the amount of vacuum from the carb. The 2100 is designed to be a strong vacuum, the stock HEI needs a weak vacuum.
But there is a simple and easy solution - match the distributor to the carb!

Get an adjustable advance diaphgram - parts stores etc. About $20. Preferably a Crane. Make sure it has a little cam like thing in the kit for limiting the total. Sometimes they get lost - some of the Chinese junk doesn't even have them.

If you don't adjust it properly your troubles will be WORSE!

Install it - the vacuum pump helps you get to the screws.

First step -- Install the limiter cam for the adjustable - it's a small piece that goes under a screw to limit total travel. Initially set it so it limits travel to about 1/3 of the total available travel. That's very important - without the limiter it can move it about 40 degrees -- waaaaaay too much.

Then through the vacuum nipple, adjust it to the LEAST SENSITIVE position -- if I remember right, that's counter clockwise - opposite of what you'd think - but look at the instruction sheet to make sure.

Do not use the mechanical weights and/or springs with it, unless you are building a street machine. You want the mechanical to come in sloooow too. Stock weights and spings work best for an off-road machine where you want low end torque. They are fine for the street too. The light springs and fast curved weights are good if you are launching at 3000 R's.

Install the distributor, time it with vac disconnected to about 8 degrees.
Connect vacuum - check to make sure the advance does not change with the line connected - vacuum should be at it's lowest point if it's the correct ported vacuum.

Check the full advance to make sure total advance is about 35 degrees at 3000. Use the limiter cam to get it in range.
Now, adjust through the nipple to get the vacuum advance so it doesn't start moving till about 1200, advances slowly and evenly to full at about 2500. You'll probably have to reset the limiter cam a couple of times.

Remember - vacuum advance readings are in addition to the mechanical, so it's best to get a "feel" for the mechanical's curve before adjusting the vacuum curve.

It takes a little trial and error, but you'll be ALL SMILES once it's dialed in!

And - a thought -- you did eliminate the resistor or resistor wire feeding the HEI - it needs full 12 volts through a heavy wire - preferably 10 Ga. It's power hungry!

Who says 258's can't turn 6000? (But don't with an unbalanced used engine.)

Enjoy!!!!

Let us know how it fares.

y2kmxz 05-21-2005 08:15 PM

Re: vacuum advance question
 
I just bought the crane cam vacuum advance unit and it does not work on a 258 distributor. The mounting holes are wrong and the shaft length is too long. This was the "Ford Kit".

y2kmxz 05-21-2005 08:22 PM

Re: vacuum advance question
 
I am going to adjust my last statement. I tried to put the crane cam kit on today and it is close but not a drop in replacement on the stock jeep distributor. Tomorrow I need to redrill the mounting holes slight on the distributor and I think it will work.

RRich 05-21-2005 08:54 PM

Re: vacuum advance question
 
Sorry - by your reply I ASSumed when you said HEI upgrade, you put a real HEI distributor in it. You must have just done the module & coil switch?

unhumen 05-22-2005 12:28 AM

Re: vacuum advance question
 
I don't know JACK S**T about HEI but I think you are barking up the wrong tree getting all twisted up about vacume.

Vacume is a direct result of throttle plate opening. You are trying to suck a given volume ( displacement of engine ) through a variable opening (carb throat)
When the throttle plate is closed as in ideling the opening is small meaning ( hopefully ) high vacume
when it is WOT Wide Open Throttle the opening is large meaning low vacume.
Ported vacume does not come into play till around 1000 rpm or so, after that manifold and ported vacume run In-Synch (And I don't mean the group) no matter how fast or slow you go untill you take your foot off the peddle.
Like I said I do not know Jack about HEI but most older engines I have tuned tell you to disconnect and plug the vacume line, so the timing is not affected by idle speed.
Are you sure you are not out by 180*

RRich 05-22-2005 01:57 AM

Re: vacuum advance question
 
""""Ported vacume does not come into play till around 1000 rpm or so,""""
True - usually.

"""""after that manifold and ported vacume run In-Synch (And I don't mean the group) no matter how fast or slow you go untill you take your foot off the peddle.""""

Maybe "in sync," but opposite.

-- Ported gets stronger the faster the R's - to about mid throttle, then drops down somewhat. At WOT it's near 0 again.
-- Manifold vacuum is strong at idle, strong at cruise, then drops under heavy load.
Totally different curves - almost opposite.

And -- there are many different types/curves of ported vacuum - depending on WHERE and HOW it's picked off the venturi bore, at the butterfly edge, above it slightly, above it even more etc, hole size, slotted or not etc.
Each slight change in position creates a different curve.

Several uses that require similar, yet different ported curves: Timing advance, EGR, Cannister purge, bowl venting, etc.

Look at a Thermo Quad - about 6-10 different vacuum nipples, each with a different function and curve.

Since his complaint is too much too soon it has to be slowed down.

Yes, if run without any vacuum, ping should go away - IF it was caused by too much advance too soon. But -- the reason vacuum is used is to advance it during light load for more efficiency - better mileage - kinda important at $2.50 a gallon.

**DONOTDELETE** 05-24-2005 09:22 PM

Re: vacuum advance question
 
Thanks for the info on the adjustable vacuum, RRich. I ordered one from Advance Auto, took them a day to get it. When it came, it had no instructions and no Allen wrench. [img]/ubbthreads/images/graemlins/smile.gif[/img] But I had the wrench and I got the instructions online, so I'm good for the moment.

I installed the advance on my lunch break, so it wasn't the most meticulous of jobs, and I didn't have a tach handy. I adjusted the advance to the least sensitive, installed it, set the cam, and timed it to 8 BTDC. I haven't had a chance to do the fine-tuning yet (had a prior engagement tonight), but I'll try to get it done in the next few days.

I was a little disappointed on the drive home... It sputtered a lot on acceleration and just ran far worse then it had recently. When I got home and opened the hood I realized that I had forgotten to reconnect the #1 spark plug wire (I have the old style spring-and-clip-on-the-spark plug style timing light, rather than the new-fangled sensor kind). Felt pretty stupid. I'll see how it runs tomorrow... [img]/ubbthreads/images/graemlins/smile.gif[/img]

y2kmxz 05-26-2005 10:58 AM

Re: vacuum advance question
 
[ QUOTE ]
Thanks for the info on the adjustable vacuum, RRich. I ordered one from Advance Auto, took them a day to get it. When it came, it had no instructions and no Allen wrench. [img]/ubbthreads/images/graemlins/smile.gif[/img] But I had the wrench and I got the instructions online, so I'm good for the moment.

I installed the advance on my lunch break, so it wasn't the most meticulous of jobs, and I didn't have a tach handy. I adjusted the advance to the least sensitive, installed it, set the cam, and timed it to 8 BTDC. I haven't had a chance to do the fine-tuning yet (had a prior engagement tonight), but I'll try to get it done in the next few days.

I was a little disappointed on the drive home... It sputtered a lot on acceleration and just ran far worse then it had recently. When I got home and opened the hood I realized that I had forgotten to reconnect the #1 spark plug wire (I have the old style spring-and-clip-on-the-spark plug style timing light, rather than the new-fangled sensor kind). Felt pretty stupid. I'll see how it runs tomorrow... [img]/ubbthreads/images/graemlins/smile.gif[/img]

[/ QUOTE ]

When you get to adjust the unit you purchased, can you post the part number? The unit I ordered from Summit Racing will not fit on the 86 distributor, I have had to autoparts stores try and locate a true adjustable replacement with no luck. If you got an adjustable, I am very interested in the info.

Last night I tried a new trick with my vacuum advance and the mc 2100 install. My jeep will ping only at cruise when I crack the throttle, no ping at WOT. I installed the vacuum delay valve and vecuum reservior original installed on my Carter Carb and it seems to have really help releave the ping. It basically dampens the vacuum response. There is not much info on the net about these valves but I keep studing the shop manual and figured it would not hurt to try. I only tested it for about 20 minutes last night but I made a run with it and without it on the same section of road under the same conditions and it reduced the ping a bunch. With an adjustable advance unit.....I feel I will be right on the money.

RRich 05-26-2005 12:04 PM

Re: vacuum advance question
 
Those valves delay the vacuum from getting through, they don't lower it, just slow it down.
The color on the end of it determines the seconds it delays it.
As I remember, they come in red, green, blue and yellow, black. They range from 5 seconds to 20 or 30? seconds. But not necesarily in that color/seconds order.
They delay the vacuum from going through - like to the advance, but they don't hold it in - so it's one way only like a check valve. Handy to have sometimes.

Yes, it can help with the "tip in". Especially the longer delay ones. But if you are holding the throttle in that spot for longer than the delay, it'll ping again.
Better than nothing though.

Interesting -- 70's Fords used them on their vacuum advance - caused an advance delay - made it stumble on acceleration sometimes.
GM same vintage had a similar stumble - caused by too fast an EGR.
Easy way to cure 2 cars - take the delay valve off the Ford and put it on the GM! Must have done hundreds. Yes, not smog legal, He He - but what smog tech would ever notice it?

y2kmxz 05-26-2005 03:31 PM

Re: vacuum advance question
 
I am going to play a bit and see what happens. I am currently running ported vacuum for the vacuum advance and my theory is that when the throttle plate cracks open the vacuum advance get the signal to advance before the motor can even respond. I have been told to try playing with the vacuum on port and manifold and the engine will tell me what it wants.

I can move to the next topic of EGR and vacuum. The 1986 258 uses a EGR that needs vacuum signal and exhaust pressure
to open. I have installed too EGR valves and can make the valve open on the test bench by blowing into the EGR port and using a vacuum pump. I can wind the motor to the moon and use a vacuum pump as the source and the EGR will not open. I am not running a cat becuase it clogged and all the pulse air stuff rotted off. Can the lack of back pressure from the lack of a cat be causing the problem?

RRich 05-26-2005 04:14 PM

Re: vacuum advance question
 
IF you use manifold vacuum: You said the ported vacuum comes in too fast and too strong. Maifold vacuum is there ALL the time! Isn't that too fast?
The only time it drops is when you are under heavy load - so does ported vacuum.

Sooo - if you use manifold vacuum it's advanced ALL the time. At cranking there isn't enough to feel, but once it starts it "sees" initial, about 8, plus the 15 or so from the vacuum advance = 23 or so. Ping city.

Try it.

Now to get it better (less worse) - leave the manifold vacuum connected - so it's advanced fully - then set initial to the 8 while it's still connected. (What that does is negate the manifold vacuum advance.)

Now as you drive it - only the mechanical does any advancing -- it'll add about 15 to the initial - giving you about 23 at cruise. Then, when you punch it or get under load, the manifold vacuum will drop, dropping timing clear back to initial - about 8! Not much power down there.
And it'll be hard to start because during cranking the manifold vacuum isn't enough to pull the advance up - so it'll be trying to start at 8-15= 7 degrees retarded. Not easy to start down there.

But - don't take my word -- TRY IT!
Most people don't understand what an engine "needs" and what the advance really does - or how it works. Lots of bad advice around.

Try those things - you'll see.

Best is get the right adjustable - or get creative - install /adapt one from a GM. Sometimes all it takes is redrilling a couple of holes.

Let us know.

Doubtful the lack of a cat reduces backpressure enough so EGR valve doesn't open. The EGR should also be running on that ported vacuum you have. The EGR will only open at higher R's anyway. To test - stuff a wet rag - wet so it doesn't catch fire - in the tailpipe - rev it - it should open.

But the trouble you are experincing is exactly as you stated in your first post - too much too soon advance.

**DONOTDELETE** 05-26-2005 06:20 PM

Re: vacuum advance question
 
Hey there y2kmxz,

I can't help you on a part number, because the vacuum advance is for a GM HEI distributor (a fun do-it-yourself upgrade). It won't fit a regular jeep distributor (as far as I know). Sorry about that...

In keeping with my busy schedule, I still haven't had a chance to tune this thing yet. Maybe this weekend... BTW, my drive-home issues were completely due to the #1 spark plug being un-plugged, it's running better than ever (though not quite perfect). Thanks again guys!

CJ Renegade 05-27-2005 09:48 AM

Re: vacuum advance question
 
When I was having problems a few weeks back (acceleration hesitation) I bought an adjustable vacuum advance from NAPA for an 86 CJ, 258, stock distributor. It took a couple days on special order. It came with a very specific set of instructions, and it was very easy to fine tune the advance (once I got the proper vac line from the carb, thanks much to RRich).
Joe

RRich 05-27-2005 04:28 PM

Re: vacuum advance question
 
Still have anything with a part number -- that would be great to know. I think that would solve lots and lots of problems that keep recurring here.
Even maybe the Howell FI ping problem.

y2kmxz 05-27-2005 09:38 PM

Re: vacuum advance question
 
[ QUOTE ]
When I was having problems a few weeks back (acceleration hesitation) I bought an adjustable vacuum advance from NAPA for an 86 CJ, 258, stock distributor. It took a couple days on special order. It came with a very specific set of instructions, and it was very easy to fine tune the advance (once I got the proper vac line from the carb, thanks much to RRich).
Joe

[/ QUOTE ]

I will have to try NAPA when I get back from the weekend....thanks for the info.

y2kmxz 05-31-2005 11:34 AM

Re: vacuum advance question
 
[ QUOTE ]
When I was having problems a few weeks back (acceleration hesitation) I bought an adjustable vacuum advance from NAPA for an 86 CJ, 258, stock distributor. It took a couple days on special order. It came with a very specific set of instructions, and it was very easy to fine tune the advance (once I got the proper vac line from the carb, thanks much to RRich).
Joe

[/ QUOTE ]

Do you have a part number for the NAPA unit. I just called the main NAPA distribution store and they can't confirm if the part they can get me is adjustable. The price is $39.95 and $5.00 shipping and it is non refundable because it is special order. Or can you confirm if this price was about what you paided.

rogerscj7 06-22-2005 07:24 PM

Re: vacuum advance question
 
Rich, or to all
I just installed the Crane Dist vac advance kit, Installed the limiter, and here are my results, do they look to be in line for the best performance?
I had a Accel, but it did not come with the limiter. Running a New HEI performance dist on my 4.2 with the Howell TBI.

Mech Advance = 12 deg @ 1400

Int timing set at 10 deg
@ 1200 i'm at 20 deg of which 12 is mech/ 8 vac
@ 1500 i'm at 25 deg of which 12 is mech / 13 vac
@ 2000 i'm at 30 deg 12 mech/18 vac
@ 2500 i'm at 35 deg 12 mech/23 vac

Should i be looking to get a slower curve in, meaning i guess to much timing to quick?


any HELP.

RRich 06-23-2005 09:44 AM

Re: vacuum advance question
 
Always with the advance light - hold the RPM to where you want, take the reading by turning the knob till the marks say 0, read the advance on the knob (or meter.) The actual timing is what the marks say PLUS what the knob says. Easy way is to make the marks say 0 and read the knob.
--- 1/2 a broken wooden clothespin makes a good ramp to use as a stop in the linkage for RPM adjustment.


Sounds like "Too much too soon" on the mechanical.

"Performance? Distributor?" Most of those are set up for drag strip use. They "pop" the advance way up almost immediatly - expecting you are going to "launch" at 6000 R's anyway. They expect you are going to rev it up unloaded to 6k, then dump the clutch. The fast advance helps you get it up to 6k fast - but not under load. At 6k the advance is all the way in anyway. At 6k the advance can be far greater than 35 too. Engine life and ping are not a problem on race engines that will only last 4 or 6 miles anyway.

They are not realistic for the street -- or especially off road. The mechanical advance uses super light springs with weights ground to advance it waaay too fast.
You have to change those so called "performance" things to make them work properly. Toss the weights and springs, use stock ones - not even the ones from a kit - get OEM STOCK. You end up with a colorful or shiney "stock" distributor - and a lighter wallet. Just shows advertising works.

Most don't even have an adjustable vacuum advance diaphram either. Save your money, use bone stock for the best performance for our purposes.
If you don't believe it - try it!

The so called "performance modules" are scam too. They simply pot the stock one inside some colored plastic.
Think about it -- do you really think they have Motorola or some other chip maker to redesign and build them a different chip for multi-millions of dollars so they can sell a limited number of them for slightly over the price of a stock module produced by the millions?
Not real. Again, save your money.


Now for what you need:
Ideally -

No vac:
Idle = 8-10
1000-1200 = advance barely starts to move
1800 = 18
2600 = 22 (Just about all in at this speed)
3000 = 25

With vac:
idle - 8-10
1000-1200 advance barely starts to move
1800 = 24
2600 = 32
3000 = 35

If you get it near that, it should perform well, start nice, and get good mileage - without excessive engine wear or ping.

Notice the mechanical moved it - or should - about 12-15 deg.
The vacuum moved it another 12-15.
The entire total - initial + mechanical + vacuum should end up around 35 degrees at about 3000. The advance systems should be "all the way in" at 3000. More than that will give driveability problems, less than that will give less gas mileage. If both the vac and mechanical are slightly too much, just drop the initial down a little, but not below 0.
Make sure the tiny pin in the slot under the weight plate has the bushing on it - stock it's rubber, aftermarket they are brass. That limits the mechanical travel.

For the techies - above 3000 the engine is straining more, ported vacuum starts to roll off, so advance actually starts lowering slightly - until it drops down totally to the power curve - set by the mechanical. That occurs about 4500-5000. Above that max power can be had by dialing even more advance, but most engines can't go much more than that. At 8000-9000 R's, it often needs in the range of 50-60 degrees!

The actual numbers are not real critical and cannot be predicted for your particular engine. But as long as the curves are smooth and they peak at about those points this should be very close.

These are generic numbers, the only way to get the exact "best curve" is with a chassis dyno under load with an exhaust analyzer, taking several measurements and experiments. Each engine - and all the related "stuff" - exhaust, intake etc - even charging system voltages and loads, are different slightly. That's why "generic."



My opinion of Accel and Bosch, and lots of other "pink" "performance" stuff - the best performance is obtained the instant you buy it - they got your money - it performed well for them, didn't it?

"Pink" -- if you want to sell something that doesn't do what you say, call it "performance," color it bright pink, bright yellow, flourescent green etc - make it colorful, kids will buy it!

Hard to tell real stuff from trash.

John_Strenk 06-24-2005 09:48 AM

Re: vacuum advance question
 
I notice in computer controlled 258 (83 on) the the vacuum advance on the distributor distributor is connected to the manifold vacuum. Is this because the computer has some control over the advance? This would explain setting the timing at 1600 RPM with the 10" and 4" vacuum switch and vacuum hose disconnected.

So if you bypass the computer you should connect the vacuum advance up to a ported vacuum connection. Right?

IS there anything else special about the distributors used on the computerised 258 we should be aware of?

CJ Renegade 06-24-2005 10:42 AM

Re: vacuum advance question
 
I went through this a couple months back. RRich has it right. His rpms and °advance are just about what I got after I switched from manifold to ported vacuum, and after I adjusted the new vacuum advance. I used all stock parts and the engine has never run better.
Sorry - I dont have the NAPA part # for my '86 258 vacuum advance, but as I recall it was about $30 and yes, a special order. It only took two days to get it. It installed easy and adjusted with an allen wrench even easier.
After going round and round about why the vac adv was plumbed to manifold vac...I even checked a second CJ, an '84, and it was plumbed the same way...I came to the conclusion that the computer must have some control over the advance.
But it works better now than ever, again, follow RRich's advice and you'll see for yourself.
Joe

LEVE 06-24-2005 10:47 AM

Re: vacuum advance question
 
[ QUOTE ]
...I even checked a second CJ, an '84, and it was plumbed the same way...I came to the conclusion that the computer must have some control over the advance....

[/ QUOTE ]

The BBD Feedback ECM does control the timing via the knock sensor...about + or - 3 degrees.

rogerscj7 06-24-2005 10:49 AM

Re: vacuum advance question
 
Hers's the Crane part # CRN-99600-1 $22.88 plus shipping.
Works great..

RRich 06-24-2005 11:10 AM

Re: vacuum advance question
 
Yes, the computer controls the advance - when equipped.
There are 2? maybe even 3 solenoids that the computer uses to switch the vacuum in and out.
Yes, base, initial timing is set mid range. They want it above idle, else it'll be set wrong.
The vacuum is manifold vacuum - used strictly as a power source, not for the vacuum curve characteristics.

So - when the computer "feels it's time" for some advance it opens the solenoids, letting the strong vacuum through to the distributer, advancing timing.

Not sure, but probaby the parameters for advance (open solenoids) are:
At operating temperature
At higher RPM
At High vacuum - indicating cruise condition
In high gear.
If all conditions are met, the solenoids open and the vacuum pulls it forward.
It may even always be open at idle too.

And criteria may also include -
When the engine is overheated
and possibly even during deceleration.

The focus of attenton with the design was emissions. Chrysler was already in trouble with the ARB and the Feds at the time.

Those are my guesses - haven't verified it though. Those are common criteria for many vehicles. There may even be one or two more!

So the effect is there is no vacuum advance until the computer says so - then suddenly it "pops in." Sometimes when driving it you can feel it come in. It's not a slow transition, but a sudden "pop" as they open.
I've seen a vacuum delay valve added to the distributor line too - not sure if that's stock or not, but it would take out some of the "pop."

Using straight direct ported vacuum allows the advance to become a function of throttle position, not at the whim of the computer.

Yes, if the computer has been disabled, rewired, Nuttered etc, then those solenoids are not going to be operated correctly by the computer. You will have no advance at all.
Rerouting to use straight manifold vacuum all the time will only cause other troubles, poor performance, ping, poor mileage etc.

Using straight manifold - as soon as the engine starts the advance will slam full and stay there. Acceleraton will be poor, probably will ping on acceleration - because timing is way too far ahead.
But that can be compensated by lowering the initial timing to 8 or so. Then acceleration will be better, still not good, but "less worse", ping will probably be inaudible (still destructive though) and poor gas mileage.
That's why some folks will say it works for them, they just don't know how good it could be.

The idea behind using ported vacuum -
Burn time in the cylinder is relativly constant, no matter what the RPM.
You want the maximum cylinder pressure to occur between 32-38 degrees AFTER TDC. That requires firing the plug with enough lead time to get it - thus timing advance.
The faster the engine turns, the more lead time needed.
There are two "ideal" curves - one for maximum power, one for maximum efficiency.
Mechanical advance follows the power curve.
Vacuum advance follows the efficiency curve.
Ported vacuum has the correct curve to provide the needed advance for the distributor.

Don't eliminate the solenoids or computer, simply reroute the vacuum hose to ported. You may need to convert back someday to pass smog inspection.

While you are at it - Disconnecting the EGR - plug the line to it, makes a big difference too.
Set initial timing to 8, no vacuum.

That's things you can do for less than $1.

Sorry, gotta do this - my disclaimer - these are not street legal modifications - off road use only.

He He -- Can I disclaim my disclaimer?

Using the right vacuum in combination with a properly jetted carb, and an ignition system worth having (Go HEI) - the little underpowered 258 really comes alive!!!

Now add some breathing modifications, like a better air intake -- that stupid restricting filter is a real joke. Try it on a test drive without the air cleaner - stay out of the dirt though. You'll see how much difference that makes too!
And - use the stock original plugs the heads were designed to use - ignore advertising bull!

It's all in the "knowing what to do," not the big $$$.

Every one I've done the owner gets that grin from ear to ear!


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