Setting Ignition Advance

My rig has a power issue, and I think it has to do with advance in my distributor. I have the 225 with an HEI conversion from a '75 buick. My initial advance is set about 12* right now, but still doesn't ping. I used to have it at about 6*, but the rig runs the same either way, so I'm leaving it at 12* for now. I just got an adjustable timing gun today, and at around 1700 rpm I'm around 22* total advance, and around 2500 rpm I'm at around 42* total advance, or if I pull the vacuum advance line off, I go down to 22* total advance. My problem is I have no power going up hills, the Jeep barely makes it up a grade of any size, and won't go above around 1300 rpm up the hill in 2nd gear at wide open throttle. Also seems to be no discernable power difference between 1/3 throttle all the way to the floor. So, how do I go about trouble shooting this to get where I need to be? I know we are supposed to be around 32* total advance, is that with the vacuum advance? and that is at what rpm? What total advance should I be at for various rpms? Any/all help is appreciated. I'd like to figure this out myself instead of taking it to a mechanic.

 

I don't have a vacuum gage, and how and where do I check for vacuum leaks? The motor revs good in the driveway out of gear. Will rev hard and fast up past 5500rpm no problem, but I can't get it over about 3400 on the street, and can't even keep it at 2000 going up hills (usually falls below 1500 going up hills on road), so I'd say it is definitely a load condition!! I don't know if I would say the carb is tuned optimally, it smells a bit rich, but the plug color when I pull the plugs is kind of skin colored, so it's good on burn rate I guess. It is the 2g on there, but it is kind of a crappy old rebuilt one. And to answer the other question, I'm at roughly 3300 ft. elevation, but drive and 4 wheel between 3000 and 4500 ft above sea level.

 

First off lets get one thing straight.the vacuam advance is a fuel economy mechanism.has absolutly nothing to do with performance.total advance is usually considered initial advance + mechanical advance = total advance. you do not add the vac. adv. into the equation.when you accelerate the manifold vac. goes down and the vac. adv. does not function.period.so total advance of 32deg. sounds reasonable.if it is less you probably have not enough mech. adv. HEI dist were notorius for to little mech. adv.sounds like you do not have enough total adv. which will definitly hurt performance.most hi-perf vehicles don't even us vac adv. My 427 ford with dual point dist. for example came from the factory w/o vac. adv. (they weren't concerned about fuel mileage).A working vac .adv. is a great fuel economy feature and should be in working order,but your barking up the wrong tree if you think it is causing prformance issues.sorry for the long post .

mike

 

sounds like something I had going on. Messed with the hei dist., carb settings. ran great at lower rpms and short high revs. Ended up being plugged fuel line just was not getting enough fuel to run. Just a thought might want to check fuel filter / fuel line Brian

 

Let me see if I’ve got this straight.
At idle you’re running timing at 12* BTDC, then at 2500 RPM advance is all in at 42* BTDC. Correct?
If so that’s maybe a bit high but sounds like your distributor is working correctly and is not your problem.
Without knowing more, look for vacuum leaks, make sure fuel filters are clean and flowing fuel, you could check the screens in the fuel inlet for your carb, I’ve actually had trash make it past the filter and clog up these screens, and I always like to read the spark plugs. They’ll tell you how everything is burning and if you have a vacuum leak your spark plugs will read lean.

http://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

 

you should probably go back and reread the first post.he said he only had 22* advanve with vac. adv. disconnected.that is not enough.

mike

 

SPARKY, when someone says total advance to me its
initial advance (static) plus
centrifigal advance (mechanical) = total advance. this is the important number for performance.then if you want to add the degrees of vacuum advance onto that great.32-34* (static plus mechanical) you must have for acceleration.the only time the vacuum advance works is on light throttle when cruising.as soon as you step on the gas pedal the vacuum drops and the timing retards.this prevents pinging.Motor's spec is 28* centrifigal with 5* static would be 33* .i would urge the man to take the distributer to a shop equiped with a distributer machine and have it setup properly and add a adjustable vacuum advance. i saw a HEI for sale just the other day that had all that and reconditioned to boot for about $200. i think everybody is on the same page just diffrent terminology.

mike

 

So, I took the Jeep in to a shop yesterday to see if they could figure out what is wrong with the Jeep. They looked at various things and checked various things, and they have come to the determination that there are possibly two things going on with the Jeep that is not allowing it to make power. They feel the timing chain is off one tooth. They say it feels like it is out of time roughly what the tooth off would cause. They said the timing is advancing well and "normally" and shouldn't be the issue. They also did a compression test, and said the lowest cylinder was at 90, the highest was just barely over 100. He said (which I thought I remembered also) that the compression test should be in the 160 range, 150 at the low end, and think about what's going on in the bottom end once it gets below 130. So, basically, he said if I do get the timing chain back on correctly, it would still be limited in power because it doesn't have the compression needed to provide any torque. This kinda sucks, because I just spent the money to put new heads on, to find out that the bottom end is potentially suffering. Also, I get lots of oil blow-by out my oil breathers and caps on my valve covers when I run the rig, which is very annoying. He said he noticed that too, and it is probably, or could be, blow by caused by the lower than desired compression. So, I really don't wanna rebuild this engine. Does anyone know how much it would be for pistons and rings, etc. with machining and labor and stuff to get the bottom end rebuilt to get compression back up? Has anyone done it recently so they know the estimated cost of the project? The mechanic said he didn't have a number for me right away, he'd have to do some research for parts costs, etc. Does my mechanic sound full of crap, or could this compression thing be the culprit? Thanks guys.

 

Backwards Mike.
When you step on the throttle and the throttle plates open then manifold vacuum drops. The vacuum advance on his engine should be hooked to ported vacuum which comes into play after the throttle plates are opened as the vacuum port is above the throttle plates.

The vacuum advance's purpose is not simply for mileage. It is also a driveability enhancer on low performance stock type engines. It increases advance as rpm increases and as the throttle plates open to keep driveability as good as possible throughout the rpm curve of the motor as well as enhancing the torque and horsepower curves.

Many high performance engines have no vacuum advance because they generally have higher compression ratios (which require higher octane fuel so can generally run higher total and or initial advance), higher idle speeds, and make their power in a much smaller curve therefore don't need the vacuum advance. Plus the performance camshafts create vacuum pulses and low vacuum at various rpm's and loads that vacuum advances can become a hindrance not a help.

TOTAL advance is initial, mechanical, AND vacuum advance. You want to know the TOTAL advance the engine is getting as well as what rpm the various advance mechanisms are working as well as initial.

A vacuum gauge is very useful for engine tuning and I should have mentioned that to Skysthelimit when he called me last weekend but my mind was elsewhere so my apologies for that.

 

Well I talked to Nickmil tonite (seems to be a more common thing lately, lol) and during the conversation realized I have a 231 intake manifold on my 225 (he thinks) because my PCV valve is located in the rear top part of the intake manifold instead of going into the valve cover like is typical of 225's. Anyway, this got us to wondering what other parts, if any, have been swapped from a 231 to the 225, either for convenience, for "performance" or for some other reason, and if any of them effect the even vs. oddfire performance characteristics.

So, on Warloch's suggestion, I will analyze my timing chain cover and see what I come up with, instead of just assuming it is stock.

Patrick, when you say valve timing being off will cause low compression, but being off one tooth probably won't, what exactly should I look for regarding the valve timing that could be off far enough to cause the low compression.

Man, it seems like no mechanics are familiar enough with the oddfire to be good help around here. I wish I had one of you guru's living in my town. I may have to tow it to Portland before too long and have Nickmil help me, as I'm really at the tip of my mechanical knowledge for this problem and try most any and everything that you guys suggest as long as I'm able to perform the work myself with the tools I have. So, thanks so much for all the advice and potential ideas guys. I'll post pics of the motor tomorrow, too, so you guys can all analyze it to see if anything looks wierd or "off" with it, like Nickmil pointing out the potential 231 intake on the thing. Maybe there is something else visually outta whack that may be the culprit that we have all taken for granted until now. I guess we'll see. Sorry for the long rambling post.

 

Taking a long shot here, but did this start with the hei being installed or has it always been there. I have seen odd-fires run with the distributor out of phase. There are several good threads covering this. Odd-fire heis have to be on the right lobe of the pick-up coil to make any power. On the intake possibilities, you can spray starting fluid on the edges of the intake where they meet the heads while it is running. If the idle increases then you could have the wrong pan gasket for that intake.

 

If the HEI were not right he would only be running on three cylinders. In the driveway it would sound great, but power would be lacking from the get go. If he can measure the amount of advance via a timing light this shouldn't be the problem... been there, done that. Otherwise the mark is going to be nowhere close to the right location.

The timing cover can be all over the board as well... personally i am running a 350 timing cover on a 231 EF block with 225 OF rotating assembly (long story). All parts interchange somewhat freely, so I'm not quite sure what the timing cover will tell you.

Compression sounds good to me... all of the 225's and 231's I've ever owned were ~120lb in compression. Latest one is at ~130 on a freshly rebuilt motor (not quite sure how well the machine work on the block was) pulling 34" LTBs up a pretty good grade on 3.73's at 60mph every morning into downtown ATL.

I also had a manifold leak on mine for a while that drove me nuts until I found it. I had trouble climbing grades and would eventually backfire out the carb... don't know if that helps you at all.