Inliners International Forums General Discussion Engines 250 Hesitation

I have posted this on two boards, so if some of you see it twice, my apologies.

My '66 Chevy has a rebuilt 250 that is stock with the exception of a Pertronix HEI. I have very few miles on the rebuilt motor. I have set the timing by sound\feel as I don't think the original numbers would be any good since I switched to HEI. I set the thing to run at the highest vacuum I can get (17-17.5)using a gauge hooked to the valve cover side of the pvc hose. It seems to idle fine and revs fine sitting in the drive, but when I take it for a spin, it hesitates and jerks when under load. When I come to a stop sign and push the clutch in, it will often die.

I have a 1bbl carb that is a rebuilt one. My plugs are AC R44xls gapped at .044

Anybody have any suggestions. I wouldn't mind switching to a different carb if that was necessary, but have some concern about my original air cleaner fitting a 2 barrel.

The truck was my grandpas, and I am trying to keep as close to stock as possible.

Thanks

I do not think that is a proper way to set your timeing.
Points,HEI,Petronics dist,does not change what your timeing should be.

Need to use a timeing light.
That would be the first thing to do.
Second,close your spark plug gap to .035.That way we might see if you ignition is cutting out under load.
After,then take it for a spin & let us know what the out come was.

MBHD

Dear Curt;

The ignition timing can be set "by ear" with points or without, but that's NOT the way to do it.

Use a light like Hank says and follow the directions in the Motors Manual for that engine. Be sure you understand the vacuum advance directions, before you start.

The spark gap and Carb are probably okay.

Good luck.

also check the power valve in the carb. make sure it squirts when you throttle up. you can check this with engine off and look into carb and watch for it to squirt when you manually work throttle linkage. also check to see if intake manifold to head gasket is leaking. way to check this is to idle engine and take a can of spray ether and spray gasket area between head & intake where gasket is. if engine revs up gasket is leaking hence the problem. these engine are notorious for leaks in the intake-exh. manifold areas.

Hei might not match the advance curve of the original. Vaccum may be on the wrong carb port. Carbs were notoriously lean and often function beter and even get better mileage with abot 2 sizes larger jet

I changed plug gap to .038, confirmed getting a good squirt when operating throttle, checked timing with a light and with vacuum advance line plugged. Timing is advanced well beyond the timing tab.Tried to retard timing by turning distributor, and couldn't get it nearly enough without killing motor and making it difficult to restart.
I did not find the motor speeding up, or slowing down when I plugged\unplugged the vacuum line. The vacuum advance is hooked to a connection on the side of the one barrel carb. It is the only connection on the carb. Should this go somewhere else?

I took the distributor back out, found TDC, which also had the timing mark on the pulley aligned with the 0 on the timing tab. I reset the distributor, and the truck started but ran pretty rough. I went out and turned the distributor slightly and it smoothed out considerably and the idle increased. When I put a timing light on it, it was at least 30 degrees beyond the timing tab. The miss is still there, and I fear the surging under load would be too.

There was a gentleman from this board that offered to help with the timing issue last year and he was from the Evansville, IN area. I REALLY need to find that guy and ask him for some help!

I remember his first name was Bill, but don't recall the last....I'll have to try to find his email address from our conversation.

If you have a stock 250 recently rebuilt you should be reading at least 20 on your vac gauge at idle with a steady needle. If 17 is the max you can get you either have late timing or a vac leak on your intake system. This could also cause you to have a surge as you stated. Also your timing marks could be off giving you an inaccurate reading. Set your timing by ear, advance it till you get the higest idle then back it off just till it slows (barely). Shut off and restart engine if it kicks back on the starter you are advanced to far. If it starts OK then drive it and see if you hear any spark knock/fuel ping if so you are advanced to much if not and you still have the surge and the low vac reading start checking for leaks (intake gaskets or carb base gasket or cracked intake or unpluged vac port or broken diaphram in vac advance. I have seen a bad distributor shaft bearing cause some weird things to happen it should have no side play that you can feel.

Good Luck

I have sprayed some starter fluid around the intake wfrom the top side while motor was running with no increase in idle. I will try from underneath tonight.

Thanks for all the help.

Dear Curt;

Are you trying to set it with the vacuum advance connected??

John,

I disconnected the vacuum line from the vacuum advance can and plugged it. Although, I will say, that with the timing light on,and the line plugged, the timing mark did move counterclockwise upon acceleration but it came back to where it was at idle. I suppose the timing would still move upon throttle even with the line plugged?

You asked once about whether the idle speeds up when disconnecting\plugging the line. I can't hear any difference in idle when I do this. The line is connected to the one and only port on the Rochester carb. Do you think maybe I need this vacuum line elsewhere?

Thanks

C;

When you "unplug" the line; can you feel/hear vacuum there?? You should and the engine should speed up when you re-connect it.

If it does not (speed up with vac) the vacuum advance can is bad and may be the cause.

Good luck.

PS: Your setting it right (line off-pluged) and you just slow the idle back down (speed screw) when the line's back on. Then smooth out with the mixture screw.

John,

If there is vacuum there, it is so small I can't hear or feel it. There are a couple of other ports on the intake. Should I try one of those?

The distributor and vacuum advance are new, although this wouldn't be the first time a new part was bad!

I'll try to take the line off and suck on it to see if the vacuum advance lever moves.That might give me some indication. Maybe I can stick a piece of paper or something up to the line to see if there is any vacuum. I sure can't feel any with my hand.

Thanks again!

Is there vacuum at the carb?? May have the wrong fitting there/line pluged. There should be a lot.

It takes a special suction pump to move the can when It's installed on the Dist. New cans are rarely N/G.

JM...

I can't wait to get home and check that. This may solve problems I have had for some time. There is a great deal of vacuum pulling thru the line for the pvc, but I don't remember any of note thru the carb line.

Thanks!

C;

There two different things.

The PCV system pulls any "blow-by" in on decelleration. The Carb. port is only for the vacuum advance mechanism.

The wrong fitting's in there, the line pluged, or something's in the vacuum port.

You'll see; when you 'clear it' etc.

Happy trails.

OK, got home and nearly ran out to the garage! The line from carb to vacuum advance is clear. I took the carb off and looked at the fitting that screws into it and the actual port. I know very little about carbs(obviously). The inside of the fitting has two very tiny holes that go into the main body of the carb and are just above the throttle plate.They are no bigger than a needle. Is that where it is supposed to draw vacuum from? Those holes are clear, but I can't see how much vacuum would be drawn thru them. The fitting is flat on one end with a small hole in the center (1/8"). It looks like if it bottomed out, it would cover the other two tiny holes because they are not centered. But, I checked the depth it screws in, and don't feel the flat part would be blocking the holes.

I'm sure that description is clear as mud! I can take some pictures later if needed.

OK, I'm going to have to admit my stupidity
I took carb off and made sure all passages were clear, remounted it etc. I started to hook the timing light back up and kind of went thru it in my head. The other day was the first time I had used one for several years. Hook two cables to battery, and then one to......oh yeah, number 1 plug wire, not the coil wire, idiot!!
That made a significant difference in my reading, but not sure how much it helped. I am way before TDC now, but can get it in the vicinity with the truck being able to run.

Oddly enough, when I did have it hooked up right, the light would have a 1 second pause in the strobe on occasion....hmmm wonder if something is up with the #1 plug or wire.

The saga will continue tomorrow

C;

Sounds like the timing is set now W/O the advance working, which is okay & the way It's done.

Now; Let's resolve the lack of vacuum at the Carbs port. Does the carb manifold gasket have holes/slots in it?? These allow vacuum from the manifold opening to the Carb. port.

It has some holes, but they didn't align perfectly. I could see a slot in the carb that appeared to lead to a hole. I trimmed a light amount from the gasket starting at one of the small holes. I could see the pattern of the slot on the gasket and followed it.

Now that I think about it, I didn't check to see if vacuum was improved after doing this. I did observe the vacuum advance arm move in and out when I throttled up and backed off.

Curt, are the holes (the two small 'pin' holes) in the fitting or the carb? The description you gave makes that sound like a timed vacuum port. Don't know if that's right for your application or not.

The pin holes are in the carb itself.

C;

Right; in the base. These 'feed' vacuum upward (internaly) to the port where the fitting is and then (via the line) to the distributer.

Your base gasket must have slots for the vacuum to get to the carb o n some models.

Make sure this passage is open too.



PS; I guess if the advance is moving It's clear.

During all this investigation I also found the throttle plate rod is leaking fuel when the accelerator is pressed. I suspect it was supposed to have new bushings when it was rebuilt, but that was skipped.

I'm thinking of going to a 2 barrel Holley Weber from Langdons with hope of making the thing all better. I like the idea of the electric choke, but realize I will have some problems with making the linkage work.I realize the merits of a single two barrel have been hashed and re-hashed on this board, but i have to ask...am I all wet in thinking this will improve driveability and simplify the matter? I'm really just looking for a nice way to drive grandpas old truck while not getting stranded.

Curt,
Maybe I'm coming out of left field on this, but I'm running crane cams set up with my distributor, and had some of the same problems it sounds like you're having when I first installed it. (I do have a Holley 390 cfm 4- bbl on my 194, but that shouldn't matter.) The crane cams set up I have is different than your pertonix but some similarities, with adjustments. I had to do some fine tuning with mine for it to run, idle, time properly. (The timing requrements didn't change any from stock requirements.) I had to "phase in" the optical trigger on mine. But I noticed on Pertronix's web site, under troubleshooting, it mentions a few things, 1) correct positioning of the Ignitor red wire, 2) the air gap between the module and magnet sleeve being too great, 3) ground wire inside the distributor is not connected, 4) wire connections are not tight, 5) polarity is not correct. Is there a manual vacuum adjustment on that distributor? I noticed that on their website as well. Possible problem areas??? Also, areas that you've probably already checked, but I'll throw them out there --good, solid-core plug wires, making sure that they are not "crossed over" one another; -- good coil, possibly heavy duty; -- also, Leo Santucci's Power Manual states that with HEI, .050 to .080 pug gaps may be used, so your .040 should be okay too. It just sounds like you are going round and round with all of the other stuff, carb adjustments, etc., maybe this will help. Good luck!
Eric

Eric,

Thanks for the thoughts. I'm going to look on their site again to see if I can find the exact gap required for the module and magnet. I can't find my old instruction sheet. All of the wire connections are tight.I'm not sure I understand what you mean by phasing in the optical trigger.

I may have misstated what I did with the distributor. I bought a new (stock) one and added the pertronixs to it, so I don't think any adjustment to it is possible. I bought new plug wires, but they were made to look like the originals female ends at distributor, black, etc. and may not be sufficient. I'll have to re-search that to see where I bought them, although I thought they were capable of handling HEI.

Some more things to think about, but certainly worth a try.

Thanks again!

I have a 64 chevy impala with a 230 in it. just ordered a holley weber carb from langdon's. It will need a reverse throttle adaptor that Tom doesn't sell. If you run into a devise that works keep it in mind. I will do the same.

Will do!

I tried turning the carb 90 degrees and was able to use my original linkage setup. Had to buy a piece of steel rod, cut to fit and thread it, but it seems to work ok. No problems in driving it, although I suppose the main issue is in cornering. I don't expect to take many curves fast in this truck anyway!

Don't know why but I just didn't care for the brushed air cleaner that came with carb. I primed and painted it gloss black to match the original, and I like it now.

After carb, I still had my miss. The plugs were fairly new, but I decided to try a little hotter plug.....no more miss!!

Drove the truck around a bit today....what a great 50th birthday present.