HD8 high idle aggravation

[steveg]

My HD8s have had this problem in the several years I've had them: idle was originally set to around 800 rpm. Driving the car, coming to a stop the idle is around 1500; then sitting at a stoplight, it will gradually settle to approximately 1000. I can blip the throttle and it'll slow to 800. The carbs are relatively new, having been rebuilt when I bought them a few years ago. Distributor rebuilt by Jeff at Advanced a few years ago.

No visible binding in the linkage.

Would appreciate ideas on what might cause this.

 

[DerekJ]

I'm pretty sure it does have something to do with the linkage and not the functioning of the carbs themselves. I had exactly the same problems with HD6s on my original 100-Six. I never did manage to eradicate it.

 

[rjc157]

It has to be in the linkage somewhere something might be slightly off ,it also could be a vacuum leak

 

[bob hughes]

I'm pretty sure it does have something to do with the linkage and not the functioning of the carbs themselves. I had exactly the same problems with HD6s on my original 100-Six. I never did manage to eradicate it.

How about trying some stiffer return springs to substantiate the linkage theory?

My HS6s are a bit iffy but I am putting it down to the fact that they have never been rebuilt and I know that there is a slightly dodgy joint on at least one of the carbs.



Bob

 

[RAC68]

Hi All,

Over the years, I can't even estimate how many times I tried adjusting the carburetors, set the linkage or even rebuilt each unit in my attempt to gain a steady idle under 900-1000 RPMs. However, since so many HD8/BJ8 owners have indicated similar experiences to my own, I tend to believe the issue is in the carburetors, intake manifold/head design, or something else inherent in the Healey's engine that can NOT be corrected by carburetor adjustment or linkage realignment.

I appreciate that Healey models previous to the BJ8 seem to be able to achieve a steady 600 RPM idle and the only obvious differences I am aware of are that they do not use HD8s and have lower compression ratios. Are there any other model differences that would cause a BJ8/HD8 to require a higher idle speed from its predecessor?

Ray (64BJ8P1)

 

[steveg]

My engine is a fairly tired 29D with high-lift rockers, a DMD manifold and Kirk headers. No internal mods. Didn't have this problem when running the HD6s.

After all this, it seems like the problem is in the carbs. Eric Grunden said he thinks the castings can change shape slightly when hot, causing the butterfly shaft to hang up.

 

[Keoke]

I agree with Ray,
if you check your idle speed indicated on the car tach against an accurate hand held unit you will generally see 1ooo RPM on the car tach is equal to about 600 to 700 RPM on an accurate instrument.

 

[DerekJ]

Ray, I would have to disagree with that. The problem being described is car specific. There are thousands of people with HD8s that have no problem with the revs 'hanging up' until the throttle is blipped. I had HD8s on my current 100-Six, with a DWR cable throttle set up and never had any problems at all. I did have the problem on a previous car with HD6s, then no problems at all with a second car with HD6s.

It is probably caused by a combination of mechanical issues, the most likely is the crazy throttle linkage system that is difficult to get exactly right, particularly as part of it is virtually inaccessible and so never gets adjusted. Problems with the butterfly shaft as mentioned above might also be a cause. Stronger springs would be worth trying as a first step.

 

[RAC68]

Derek,

I may have confused everything. The throttle hang-up is, I believe, a mechanical issue with either the linkage or carburetor throttle plates hanging up. The issue I was focused on was what I believe is the inherent high idle reading of the HD8/BJ8 that is not caused by a sticky throttle.

Although I agree with your assessment for the most part, another issue I have experienced that has caused high irregular idle speeds requiring a blip of the throttle is a sticky choke. My BJ8 came through with 1 chock spring hooked to frame and attached to a "Y" piece of wire that pulled down on the choke levers. Although this seemed to work rather well, it required a strong pull of the choke for actuation and, over years, became inefficient in pulling off both chokes. As a result, one choke was left slightly on (usually the rear) leaving that HD8 running a little rich.

To address this choke release issue, I followed a friend's advice and purchased 2 springs that I installed on the actuation cable of each choke to push the lever to the closed position. Although this did solve the issue, it make pulling the choke even harder when reaching through the steering wheel so I returned to the single spring and "Y" wire with the occasional requirement to get out of the car and push the rear choke home by hand. Although it would be nice to find a correction for this issue, I have put up with it for more then 50 years and expect will continue.

Ray (64BJ8P1)

 

[steveg]

My throttle issues do not involve the chokes. I fixed that by replacing the cable housings with teflon-lined bicycle cable housing and used setscrews at both ends to secure the housing from moving. See: https://www.pbase.com/stevegerow/image/109638552

I suppose it's possible the linkage is involved but have never seen any indication. With the carbs off the car, the butterflies seem to seat properly every time.
My feeling is my particular problem is internal to the carburetor.

Possibly the next step would be to remove the carbs and heat them in a 175 degree oven to see if anything changes in the operation of the butterfly. Way too much trouble.

 

[why]

how about just squirting every possible place in linkage with a WD-40 like product cause its so easy to do and who knows, maybe?

 

[TimK]

Just wanted to say I've lived with this on my HD6's for 34 years. I'd like to learn of a solution.