Runs rough when taking off from stop when hot

I have an original factory V8 with a 3.5L Rover engine, Holley carb and JW inlet manifold.

When the engine has been running for 15-20 minutes and I am taking off from a stop, or in 2nd going round a sharp corner (and therefore revs are lower when dis-engaging the clutch) the engine stutters (not misfire, its as if I have not released the clutch properly) and then runs ok as I press the accelerator harder. If I have the revs higher as I take off, it doesn't happen. The temp guage is at "N" or just above, oil pressure is between 20-40 (rises to 40 again as you regain speed, so this appears normal)

These are the possible culprits :

1. fuel vaporisation (a mechanic has told me that this is unlikely, but I'm not sure)
2. carburettor problem (why only when hot??)
3. something in the diff. or the clutch that gets upset when hot - or something else that gets upset when hot
4. faulty spark leads
5. distributor/points problem

Other info - I know that the engine is only firing on 7 some of the time and I have a suspicion that the engine is running over rich (plugs have dry fouling-but this may be from running in traffic)

Any help would be appreciated !!!

Likely as not it's that Holley carb. I hate to say that, lots of people like them and I used to myself, but they can be quirky and that's what it sounds like to me. To get the thing running like it should you really need to find an old time hot rodder who has lots of experience with them and have him take a look at it. Someone who really knows their stuff should be able to take one ride in it and tell you where to look.

Sorry that's all the help I can give you, I'm done with carbs, and Holleys especially. I fought them way longer than I ever should have. But a couple of things that might help would be jet extension tubes and vent whistles. You DO have center hung floats, right?

Jim - Thanks for your reply. Not sure if I have centre-hung floats or not. How would I know ?

I've been reading a lot about the Holley and am considering upgrading to a Weber 500 (a.k.a Edelbrock in the USA?) and putting in a mallory distributor (uses double points?)

The side hung float has the level adjustment on a corner of the float bowl. Center hung floats are deeper and have the adjustment on the end in the middle. They are much better in corners. I've heard good things about the edelbrock carb, had good lock with the one I put on the RV, but have also heard one report of trouble in the turns so choose carefully. I would have thought some of the carb guys would have jumped in here by now. Best of luck with it.

Jim

I had an Edelbrock on a Landcruiser that I swapped a Chevy 350 into....never really cornered that hard in it (not the intended purpose) but did have it in just about every position but upside down (thank God) and never had a problem with it.

My guess would be a mixture problem. Maybe dumping too much full when you take off??

Bill - any idea why this would only happen when the car has been running for a while. It runs smooth as when cool/warming up?

Not sure...I would think it would have to be a lot hotter for it to vapor lock. I'm no expert but I would check mixture and maybe timing or if your distributor is advancing as it should. The fouling would make me think that it was running rich in any case, but the stumbling could be an ignition problem. I'm sure others more experianced than I will chime in soon.

When the engine warming up it wants and needs a rich mixture. Once warn it no longer needs the rich mixture. If it is running a little rich then is would act up when warmed up.
Does the choke set or does it start from col without the choke? If no choke then it is rich.

Steve

Steve - that sounds like it makes sense. There's no choke in the car, and there is dry fouling, so that might be the problem. If I can find out how to make it run leaner (and hopefully still start it) I'll try that and let you know how I get on.

Hi Conor. Could you post a pic of one of your "dry fouling" plugs. That would tell us a lot. The carb may actually be too lean, and when it's cold the choke or whatever cold enrichment circuit it has is masking the condition, so when the motor warms up and the enrichment is gone it's back to a lean condition: the float level may be too low. This would explain the hesitation in corners as the fuel would slosh and the level in the float bowl would be even lower. Pressing the gas further when it does stumble would bring the accelerator pump/enrichment circuit into play and mask it again. Not sure about your fouling, need to see a pic. As to your miss, better do a diagnostic, maybe change dist. cap and plug wires. I have a lot of carb experience, but not on Holleys. I'm definitely doing efi on mine, been driving efi cars since '84, no problems.
James

If the distributor is an issue, you'd experience problems all the time. If that's the case, you MUST get that fixed before you can even consider getting the fuel mixture correct! An improper spark causes a rich condition, not necessarily at all rpms though. I'd suggest an electronic conversion in your original points distributor over a dual-point distributor! Its much simpler than trying to properly adjust dual points, and lower maintenance. Its probably cheaper and fits better under the bonnet too!

After three months (on and off !!) I have finally found the source of this problem. I discovered through someone pointing out that my engine was not the original factory engine and was in fact an SD1 engine. It also became apparent that I was using the wrong plugs, it had the short reach plugs installed and it its quite likely that the wrong plugs have been used in that car by the prevoius owner and the one before that!

I installed a set of NGK BP6ES and was disappointed to see only a minor improvement in the situation. Having gone down numberous other blind alleys, I decided to check the new plugs to see what their condition was. (I have also dumped the Holley 390 in favour of an edelbrock 500). I was shocked to find that some of the plugs were actually loose - and I distinctly remember tightening them quite well. The answer to this riddle was that becasue the short reach plugs had only gone 3/4s down the threads, the remainder of the threads were grimed up and needed some persuasion (gentle! ) to move in the rest of the way, with the aid of some copper grease. I just got them installed properly this evening and the difference is incredible ! the idle is much smoother (had to fiddle with the carb. for this), acceleration is much better and the stumbling / hesitation is now completely gone when the engine is warmed up.....