Stalls When Hot

[Goss]

I haven't found enough spare time to delve into the carbs to date but will have to start in the next few days. I did try to adjust the idle screw on the rear carb but it was locked solid, had to use heat on it to release it so suspect these carbs are sticky inside. Quite possibly this circuit is blocked.

I rebuild carbs for enthusiasts of the Honda CBX 1000 six that has six carbs that are CV and 3 circuit so it shouldn't be too challenging.

Will keep you posted.

Regards

Goss

[Tintin]

I'm very surprised to read that heat had to be used to release the idle screw on a carb that was "rebuilt 10,000 miles ago". Unless you know and can trust the quality of the "rebuild" work it might be as well to discount the earlier rebuild and start from scratch!

Robbie

[Goss]

I'm very surprised to read that heat had to be used to release the idle screw on a carb that was "rebuilt 10,000 miles ago". Unless you know and can trust the quality of the "rebuild" work it might be as well to discount the earlier rebuild and start from scratch!

Robbie

Yes, 10,000 miles and 18 years in October in which time it has not moved so I'm not surprised.

Regards

Goss

[ChrisDixon]

I have experienced a similar issue with the idle decreasing to the point where it would sometimes stall when the clutch was depressed, although this has improved significantly since I serviced the carbs and fiddled with the pedal linkage. Not a full rebuild just cleaned them up, fitted new gaskets and re-tuned them, using the basic settings and the piston lift pin. The front carb tends to run richer than the rear, maybe due to slight AED leakage. Hot starting continues to be hit and miss though.

[Goss]

I have experienced a similar issue with the idle decreasing to the point where it would sometimes stall when the clutch was depressed, although this has improved significantly since I serviced the carbs and fiddled with the pedal linkage. Not a full rebuild just cleaned them up, fitted new gaskets and re-tuned them, using the basic settings and the piston lift pin. The front carb tends to run richer than the rear, maybe due to slight AED leakage. Hot starting continues to be hit and miss though.

Hello Chris,

I know from the Honda carbs that I rebuild that they are no longer set up to original factory settings due to the less potent modern fuels (addition of Ethanol) which means they run too lean on tick over (1.5 turns out now 2.5 turns). This circuit does supply fuel constantly throughout the rev range so I am looking to set up using a Gunson's Colourtune which was used when first set up. I guess the adjustment of the idle mixture when the engine is hot would solve the hot start problem?

Regards

Goss

[ChrisDixon]

I know from the Honda carbs that I rebuild that they are no longer set up to original factory settings due to the less potent modern fuels (addition of Ethanol) which means they run too lean on tick over (1.5 turns out now 2.5 turns). This circuit does supply fuel constantly throughout the rev range so I am looking to set up using a Gunson's Colourtune which was used when first set up. I guess the adjustment of the idle mixture when the engine is hot would solve the hot start problem?

If the engine idles ok once it has been started, then it isn't necessarily the idle mixture? I put an octance booster in regular unleaded fuel, others advocate Shell Ultimate with or without an additive. I did observe that I had to adjust the screws out some way from the basic settings, and the rear carb ran leaner. Some of this could be due to wear in the carbs (but this should have less impact at idle because the throttle discs are closed and take up some of the slack in the spindles) and slight AED leakage. Also hot starting technique, do you try at first with the throttles closed or press the accelerator part way before attempting to start? You tend to learn what works for your car, but again there can be a difference between a hot start after a couple of minutes to one where the engine has cooled a little. I set my car up without any tuning aids but I have since acquired a Colortune and Carbalancer and I look forward to seeing whether they help with tuning any more than the piston lift technique!

[Goss]

Update:

Mid last year I removed my carbs and completely stripped them down, I vapour blasted the bodies (I have the equipment) then reassembled the carbs using genuine kits that I purchased from Southern Carburettors near Gatwick. I tuned the carbs using the hiss method then fine tuned using a Colour Tune. The car now runs perfectly, it pulls like a train!

What was wrong with the carbs? They were filthy internally with lots of fuel varnish that has built up over the years and I think the replacing the throttle shaft seals has made a small difference as did replacing the main jets as the rubber diaphragms were not as supple as the replacements and one had a slight distortion. All in all I think quite a few subtle issues added up so my conclusion is that these carbs need a little TLC every few years to keep them super efficient.

Only niggle now is the AED Jet needs adjustment for cold starts as I think its a little lean at the moment but that is a simple job.

Hope this helps.

Regards

Goss