24 replies to this topic

[cal844]

You dont want to go too heavy though as it will affect the boost capabilities. You might end up mixing oil weights to get a good balance as a last resort

[ACDodd]

Thicker oil.

Ac

[GraemeC]

...and put the turbo dizzy back in first.

When problem solving if a change doesn't fix the issue, undo it.  That way you are always working from a baseline.  If you don't then you run the risk of masking the problem, making things worse or just creating another problem.

[Glun34]

Ok, put some thicker 20W50 in there this afternoon and it had the same problem again! Any reasonably quick movements with the throttle and it would lean out straight away. I did just out of interest put some 3 in one into the dashpot after that to see what would happen and again of course I had the same problem. 

 

So now im at the point were I have a rebuilt carb so I know thats good, brand new pressure regulator so in theory should be good, new fuel pump so I know thats not the issue and I have checked the plenum and it all looks fine and unblocked.

 

My 2 theories now are the fuel pressure from the regulator isn't constant and fluctuates between 4psi and 3psi, so is there a block in the fuel system? That however wouldn't make sense from the way I understand it is that the float bowl would need to be empty for it to be totally lean and bog down? Second theory is that I have a leak somewhere after the carb. Has anyone had experience of a leak from the servo connection on the inlet manifold? what is the best way to check for a leak in general?

 

Unfortunately it seems I have a more underlying issue that just dashpot oil or needle profile.

 

Cheers for all the input, its much appreciated!  

Edited by Glun34, 31 March 2020 - 10:57 PM.

[absx2]

Did you put fresh fuel in ?

[Glun34]

Yes I should have mentioned, tank drained and fresh fuel now in.

[gazza82]

What dashpot spring have you got? I think there are three different types which would suggest different "weights"? So a stiffer one would slow down the piston lift ..

 

Have you checked if the piston drops correctly and isn't too worn or damaged? People use some daft things to clean up the dashpot and piston and this could mean the tolerances are too wide and it moves to easily ..

[Glun34]

What dashpot spring have you got? I think there are three different types which would suggest different "weights"? So a stiffer one would slow down the piston lift ..

 

Have you checked if the piston drops correctly and isn't too worn or damaged? People use some daft things to clean up the dashpot and piston and this could mean the tolerances are too wide and it moves to easily ..

 

Its a yellow spring, which I believe is the standard turbo turbo spring. I've had an unmarked one in there before which is quite a lot stiffer than the yellow spring and the problem is still there.

 

When I had the plenum off yesterday I had a feel how much resistance there was in the dashpot. With the 5w30 in there the dashpot would drop down pretty quickly and with the thicker 20w50 it took quite a bit longer to drop down. Both felt good pushing the dashpot up with quite a bit of resistance in it.

 

The only thing I did see was the damper is a bit worn, not sure how much of a difference this would make to my specific issue?

[Glun34]

So today I tired blocking off the servo connection on the manifold to see if it was leaking, but still the same issue. Goes lean at any sight of quick throttle usage. Then got out some vacuum gauges I have for balancing bike cabs and connected one to the dizzy vacuum advance connection on the top of the carb. Saw no drop on vacuum on throttle so I can only guess from that there’s no leak in system.

Should I try the next needle up from a BDD? Does anyone know what that would be? Is it also worth trying a stiffer dashpot spring?

[DamoMini]

Shouldn’t the vacuum drop or change as you open the throttle?

Edited by DamoMini, 03 April 2020 - 01:04 AM.