The Stovebolt Site Forums The Shop Area Engine Shop 250 Hesitation

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 had the same problem and it was the coil not supplying enough voltage to the system. Bad wires will do the same. Wait till dark. Let your eyes get accustomed to it then start your engine and check to see if there is any arcing out of the wires somewhere either on the engine or the fuel pump ot other wires nearby. If so, change them with a good heavy duty wire. I use MSD. They cost more but worth it. Also had cracked caps cause problems. Sometimes you can't see the crack. Look for carbon tracing inside the cap. It is definately ignition problems. You could also have a bad wire to the coil supplying the 12 volts to it. If you have a balast resistor in circuit, remove it. You don't need it on HEI. Do you have an HEI coil? A stock one won't be enough to power it properly. MSD coils are not expensive. Are you using a square style in the cap or a standard round type? Make sure it is an HEI coil! I hope this helps.

OOOPSSS, If you don't have an HEI coil the gap you have it too large. The stock coil can't cross the gap with enough power to run down the road. Go back to the .035 if you have a stock coil. Like I mentioned you need an HEI coil or should have one. Then you can open the gap to about .045. You have to play around with them to find the best gap. Just an extra tid bit of info.

Henry,
The coil is from Pertronix at the same time I purchased the conversion parts from them. The plug wires are from them also, and while they are supposed to be ok for HEI, they could be the problem, as I bought ones that look like stock, so they are not very large.

I checked the supply wire last night and I have 12.3 volts with the ignition switch on.

I'll try looking after dark tonight for leaks.

The timing marks work the same for elec. ign as points. Set it about 6 degrees with the vacuum unhooked. Read the plugs. After a drive, pull a plug or 2 & see if there is carbon on them. That would indicate a rich mixture. Many rebuilt carbs are right. First make shure the vacuum hole in the base of the carb has a passage in the gasket to go to the manifold. You can pull the top off the carb & check the float level. Did you use a conversion kit or complete dist.?

I used complete distributor form Pertronix. It is one of the small ones like the stock look. I had problems with the timing when I first started....backfiring, I pulled the distr. and started over. I could never get the truck to run at less than 10 degrees.

Yhe plugs are definitely carboned up. I suspected that was from having to manual choke for startup.

I think your carb. is too rich. You might check the things previously suggested.

How would I adjust this carb? There is only one screw on the thing.

OK, so I checked some of the things....
1. Took carb off base and confirmed hole\passage thru gasket to manifold.
2. Confirmed I was getting a good squirt into carb when I pulled throttle back.
3. Checked timing with gun. Found the timing to be well advanced beyond the mark, but could not keep truck running or start it when I tried to bring it back into time by turning the distributor.
3. Timing was checked with the vacuum advance plugged, although I saw no noticeable difference in idle speed when it was disconnected\reconnected.

I'm thinking I need to start back to square one with the timing. I have a definite miss at idle, and there is still the issue of running rough under load. I hate to think about this, as it is difficult to find top dead center with one person doing the work!

I pulled the distributor, found TDC, which also was the mark on the pulley aligned with the o on the timing tab. I reset the distributor, and the truck started, but ran somewhat rough. I adjusted the distributor location slightly, and it smoothed out, except for the occasional miss. When I looked at the light, it showed the timing as at least 30 degrees advanced. It was well beyond the timing tab which just goes to 8 degrees.

Am I missing something here? Is it possible that when Jasper remanufactured this motor that they assembled something wrong with regards to the cam?

I'm baffled.

Did you find TDC by the piston method or valves. If you get TDC you could put new marks on the damper. You probable will just have to time it by trial & error. It,s very doughtful the rebuilder got the cam off. It would barely run if that was the case. Jaspers puts out some good stuff. The occasional miss is probably from carbon on the plugs. To adjust the idle mixture, with the engine at an idle slowly turn the idle jet in till the engine slows down. Then back it out enough to smooth it out, usually about 1/2 turn.

You're probably right on the carbon. The plugs carboned up with less than 10 minutes of running!

My method for TDC wasn't real precise. I had a hand starter switch and took the #1 plug out and bumped the switch till I felt pressure at the hole. I could then see the piston top and hand turned the motor till it was at the very top and starting back down.

I found the remanufactured carburetor was leaking at the throttle shaft today.I broke down and ordered a Holley Weber 2 barrel from Langdons. I'm sure my next postings will be dealing with the linkage for that.

I am going to pull the valve cover and confirm all the valves are opening\closing properly before that install.

not to argue with anyone the later shop manuals show more adv timing for hei i believe, not 30 deg though. my rebuilt 250 runs more even more advanced like you stated. i have checked tdc and i don't know why it is but it is right on the balancer mark. i used a sealed power cam. can you set the timing where it runs good even if it shows more advanced?? just wondering. i will follow this thread i have been wondering about mine fore years, it has no hesitation though. good luck i hope you find your answer so i will know as well.