Dhla 45s, front carb vacuum real high back carb fine. Solution ??

[s1guy]

Morgan Carbtune hooked up after rebuild and front carb vacuum pegged on the carbtune. Back carb is good. Thoughts ???

[Sparky]

If you're using a Carbtune, I'm assuming you know how to adjust the carbs to achieve balance.  Have you tried any adjustments?

[s1guy]

Yes Sparky i know how to set them up. Just cant get front carb vacuum down to start balancing them. 

[Sparky]

In that case, maybe a compression test to exclude the really bad stuff?

[Lotusfab]

Is the screw linking the two carbs way out or slipped off so one carb is far more open than the other, preventing correct adjustment?

[s1guy]

Sparky. Just did a valve job and new head gasket. Compression great on all 4

[Sparky]

Ah, sorry, misunderstood.  Have the carbs also been rebuilt?

[s1guy]

Yes carbs have all new gaskets o rings and acelerator pump diaphrams. Eurocarb kit. 

Lotusfab, Just checked and both screws are on the throttle balance lever correctly. Hmmm

[Sparky]

I assume you've already checked what Fab suggested.  Did you have the shafts out?  Butterfly issue?

[s1guy]

Sparky, Didn't have the shafts out but will check the butterflies tday. 

[s1guy]

Going to swap the vacuum tubes on the carbtune just to rule that out next. 

[s1guy]

Ok checked mounting plates and manifold for leaks. No leaks. Rear carb vacuum is good. Nothing i do will bring the vacuum on the front carb down. When i give it some gas it comes down a bit but at idle the vacuum on the carbtune is pegged. Throttle plates ??

[910Esprit]

If I read your post correctly you seem to be saying you have too much vacuum on the front carb?   If so, I reckon its could simply be linkage adjustment.

[s1guy]

910esprit, even if i pull the front carb balance lever back the vacuum is pegged. It seems as if the throttle plates aren't closing all the way. 

[Sparky]

I'd definitely be aiming at adjustment linkage or butterflies.

[s1guy]

Sparky i,m thinking butterflies. Carbs coming off now. 

[Steve V8]

Valve clearances checked?

[s1guy]

Yes Steve V8. All good there. 

[s1guy]

This is still what i got. Not good. 

[drdoom]

Is it possible we've been looking at this from the wrong end? Perhaps the trouble is with the aft carb or cylinders, as I do not see how a high vacuum level is reflective of a defect. If, in fact, there is a sub-par vacuum level on the aft inlet tract would it not conform with the measurements seen in this case? 

[s1guy]

drdoom, you could be right. Now how do i raise the vacuum on the aft carb ??

Edited June 3, 2021 by s1guy

[Steve V8]

2 hours ago, s1guy said:

This is still what i got. Not good. 

I'm not familiar with carbtune, I use vacuum gauges, (on multi carb bikes not Lotus) balance is normally achieved at tickover, but I notice from your video on throttle your mercury is dropping where I would expect to see it rise.

[Lotusfab]

Sorry didn’t read your previous post, so have revised this post! To me it looks as if the balance is way off. Two cylinders appear to be doing all the work! Solution close the air corrector screws, adjust linkage screw between the carbs to reduce the vacuum on the left two channels. If its not the linkage are all the cylinders firing? Pull the plug leads off on at a time. You may find the engine is just running on one carb, which would explain the above. Don’t worry if your engine has been running ok up until now its probably just an adjustment issue. 

 

[Lotusfab]

Two cylinders may not fire if the mixture is wrong, one carb is blocked or the linkage adjustment is way off. Bring the idle down as slow as possible to reduce the vacuum and make finer adjustments. If its idling too fastbits very tricky to see the effect of changes.

[s1guy]

Thanks Lotusfab i,ll try that next. By air corrector you mean air bleed screws ? I have all 4 closed now. 

Edited June 3, 2021 by s1guy