HD8 Carbs Do Not Return to Idle

[Rabbits 32]

Hi All,

I have a carburettor problem that is driving me around the bend.

I sent my 1964 BJ8 HD8 carbies to the best carby restoration company in Australia as my car had high idle speeds when running which I couldn’t get down by adjustment. Reports from the repairer said that the brass bushes were severely worn and they totally rebuilt both carbies replacing just about everything in both.

I got them back and its now worse with the engine holding whatever revs I take it up to while going through the gears once it heats up to 165 degrees, strangely it is OK will the engine is cold. Eg if I rev to 3000 revs into 3rd then the engine revs stay at 3000 revs unless I push the clutch in and ‘blip’ the accelerator. It holds even the slightest increase in revs and is near impossible to drive.

Even though the carbies still stick after disconnecting the linkages altogether, I pulled the linkages out and rebushed/ refurbished everything. Adding spring pressure to the return springs only makes it worse. Additional springs make it worse. I have sent the carbies back (twice) and the repairers found that it had a bent butterfly shaft and replaced shafts and bushes.

I got them back and fitted them and they are no better.

I fitted another set of carbies of a unfinished restoration that had been rebuilt by the same company and the car ran fine.

Wayne

 

[BobHaskell]

Have you done a dashpot drop test? University Motors - Matching SU Air Pistons

 

[AUSMHLY]

Hi All,

I have a carburettor problem that is driving me around the bend.

I sent my 1964 BJ8 HD8 carbies to the best carby restoration company in Australia as my car had high idle speeds when running which I couldn’t get down by adjustment. Reports from the repairer said that the brass bushes were severely worn and they totally rebuilt both carbies replacing just about everything in both.

I have sent the carbies back (twice) and the repairers found that it had a bent butterfly shaft and replaced shafts and bushes.

I got them back and fitted them and they are no better.

I fitted another set of carbies of a unfinished restoration that had been rebuilt by the same company and the car ran fine.

Wayne

I feel your pain Wayne. Seems like this shop isn't the "best"...on confirming everything as been addressed.

One would think that the first time a total rebuild would do it.
You send them back to find a bent butterfly shaft. How did that get overlooked?

"I fitted another set of carbies of a unfinished restoration that had been rebuilt by the same company and the car ran fine."
If you have the time, I'd keep sending them back to them. 3 times now? If your shipping them, I'd have them pay for shipping both ways. That may be the incentive for better quality control. I'd also point out to them that you're using them because your understanding is they are the best. Point out you've tried another set they rebuilt that worked as intended.

PS. have you checked you timing?

Best of luck.

 

[Michael Oritt]

The vacuum advance could also be a culprit.

BTW in what manner did the additional return spring tension/number make things "worse"?

 

[Rabbits 32]

one of the questions/suggestions asked if the carby base was distorting with heat which led me to follow this line of thought. Using a laser thermometer, I was able to work out that the back end of the rear carby butterfly shaft was getting hotter than any other part of both shafts when the engine reached 165 degrees. (It is normal that this area builds up heat in a big Healey as the fan tends to blow heat into the area, however my car runs at around 165 degrees normally which is not very hot for a Healey. )

I reasoned that on my car, the additional heat on the butterfly shaft and presumably the butterfly itself led to some expansion of one or both when the butterfly was nearing closure and that while the return springs are supposed to rotate the butterfly shafts to close, the final movement of the shaft was lateral instead and figured that lengthening the arm holding the spring would improve the rotational movement of the shaft and reduce the lateral movement. This worked in closing the butterfly all the way when releasing the accelerator and the car drives normally again.

This solved the end problem but I still don't understand why the shaft is getting hotter and I will work more to see if I can reduce the heat around the rear carby, possibly by increasing the insulation on the top of the heat shield and/ or additional heat resistant gaskets between the carbies and manifold (which has already been ceramic coated to reduce heat). I have had other Healeys that ran much hotter then this one and never had this problem before so I am leaning towards it being a flaw in the carburetor base. the company that rebuilt them has offered to rebuild them with replacement bases if it continues to be an issue.