Twin 34 ICT's installed - keeps spluttering and cutting out

[StuF]

I have just finished installing a pair of Weber 34 ICT carbs to my 1600cc aircooled engine running electronic ignition from a vac advance dizzy which has had the timing checked and is less than 2 months old.

I re-jetted the carbs using parts from Eurocarb
Now have F6 Emulsion tubes to replace the oversized F78's
2 x 150 Main Jets to replace the 140's fitted
Idle jets 55's

Have balanced both of the carbs with assistance of a airflow meter and also have the manifolds tapped and balance pipe fitted behind the fan shroud.

CSP bellcrank linkage is installed and correctly adjusted to give full opening of the throttle.

I am running an Antipulse valve (arrow towards carbs) from the dizzy to a t-piece and off to both carbs - have checked the vac advance and it is all working correctly.

The engine starts easily when cold or hot, idles correctly and revs cleanly when not under load however when on the road out of first gear it splutters, coughs, misses and eventually dies. Has no power and wont rev.
Once I have come to a stop the bus starts again and revs cleanly until you get going again where it repeats.

We have checked the fuel pressure and adjusted it to 3psi through my Malpassi fuel pressure regulator.

All the ht leads appear to be tight and the coils resistance checks out within spec.

The carbs have been checked for air-leaks and new gaskets and seals have been used in the install.

Anyone have an idea why it would keep bogging down and running poorly when under load? Cant really think of anything else?
Adam and I spent a couple of hours this eve setting up the carb linkage, mixture and idle but out on the road you cant go more than 100meters without it spluttering to a stop

Pic of the engine

 

[gvee]

Sounds like fuel starvation to me.

Check your lines, filter and pump are all in good order!

Pop the pipe off the carb side of the pump and put the end in a bottle. Get someone to crank the engine and watch how much is coming out and how much of a spurt you are getting.

 

[StuF]

Cheers for the input George
All the fuel lines from the tank back are new - freshly installed R9 hose from M7 including a shiny new fuel filter!

Will check the delivery of fuel to each carb tomorrow just to rule out any "plumbing" issues I may have introduced.

Going to fit a fresh set of HT leads too as these are the only things left to change!

 

[gvee]

Can't see all the pipe routes but you might have a kink.

I guess an easy test is to sit out of gear with the throttle open wide and see if it eventually cuts out..?

 

[gvee]

Just looking at the image again... Your filter isn't full but it looks like the take off is at the top..?

 

[StuF]

Fuel pressure regulator input from the stock pump is to the rear with the outlet at the front which is then t-pieced off to each carb at the correct pressure.

The bus was left running for over 15 mins whilst we balanced the carbs and set the mixture - ran cleanly and revved up fine without any stuttering or hesitation. Only under load on the road does it shudder and die!

Might have to remove the carbs again and check the main jets arent the issue - am I correct to assume in idle conditions and without load they only use the idle jets opposed to the mains?

 

[gvee]

Idling and a little revving might not be enough to starve it. Chuck it on full tilt and watch the fuel filter.

 

[67westy]

Idling and a little revving might not be enough to starve it. Chuck it on full tilt and watch the fuel filter.

Good point in the filter. When I had mine at the garage they said it should really be mounted lower than the pump to avoid airlocks. Probably more chance of getting an airlock with the filter version as there is more space.

 

[toxicbug66]

Mucky Green (Laurie Petit) over on VZI recommends the following on a stock 1600 TP motor.

150 main jets, F3 or F6 emulsions, 170/175 air jets and 55 idles.

"Most" running issues are down to jetting on ICT's.

Rich

 

[StuF]

Mucky Green (Laurie Petit) over on VZI recommends the following on a stock 1600 TP motor.

150 main jets, F3 or F6 emulsions, 170/175 air jets and 55 idles.

"Most" running issues are down to jetting on ICT's.

Rich

Yep - spent quite a bit getting them jetted as above to try and avoid running issues
Only difference is I have 165 Air Correctors instead of 170/175 all the rest is the same

Hoping its a fuel issue or a case of swapping my old 009 dizzy back in
Had to cancel my mot today too as it wouldnt have made it to the test centre!

 

[matt-me]

I had a slight air lock once in the pipe from the pump to the twin carbs, or one of the carbs, can't remember. I think i just blew it out (with me mouth). As above check fuel is getting to both carbs.

al

 

[StuF]

Hi all and many thanks for all the great advise - managed to spend a few hours on the bus over the last 2 days and appear to have resolved the situation.

I removed the right hand carb and found the balance pipe tap from the manifold had pulled the threads out and wasnt making any sort of seal (EMPI metal appears to be made of cheese) - obviously creating a massive issue when under load, also two of the HT leads had seen better days and needed replacing.

In-conjunction with this I also removed my malpassi fuel pressure regulator and put a direct feed from the fuel pump to a t-piece and off to the carbs.

Been out for a drive this eve and it pulls like a train, revs cleanly and shoots up the hills like aren't there!

Tomorrows job is to refit the pressure regulator and retest hoping for an unchanged performance - as there was a rather large BANG from my VS exhaust when I turned the bus off, obviously some unburnt fuel was pushed through due to the standard pump giving the carbs too much pressure!

Bring on Dubs@TheCastle! 8)

 

[K@rlos]

I built an engine with ICT's over the winter with the same issue, went up an idle jet size and its fine now.

 

[StuF]

After the engine performing brilliantly last night after refitting the fuel pressure regulator it is running terrible again
I think it is the way I have mounted it as the engine vibration appears to be causing air bubbles to enter the fuel lines and cause the stuttering and cutting out
Need to fabricate a different bracket, get some more fuel hose and relocate the filter away from the vibration and see how it performs then!
Never a simple fix!

 

[gvee]

Think about the position of the fuel tank exit and where you've mounted the filter. Your stock pump needs a little gravity to help it and the filter has added a massive amount of resistance!

Either need to relocate lower or go for a leccy pump with a bit more oomph.

 

[gvee]

I run a pump like the one for sale here for my twin 34s: http://forum.earlybay.com/viewtopic.php?f=27&t=66800" onclick="window.open(this.href);return false;

 

[StuF]

Cheers for the info George - checked my mechanical pump this eve and it is kicking out plenty of pressure so wont be going down the electric route just yet
However have fabricated a nice little bracket and relocated the pressure regulator away from vibration and at a lower height
Test drive tomorrow as I need some wine this eve

Some pics of my alterations





Fingers crossed it runs well tomorrow - need to get a MOT sorted before Dubs@Castle! :shock:

 

[ozziedog]

Stu buddy, how ya doin ? Can I ask you if you spent a little time with your float levels ? And also check the float needle valves, just by blowing against them, might be worth looking at the floats as well and give them a little shake next to your shell like and if you still ain`t sure, submerge them in a bowl of water and turn them over and over and look for bubbles like when you was fixing punctures on your bike I`m thinking starvation but if they`re holed that won`t be it but it could then be the opposite :?

Ozziedog,,,,,,,,,,,,, All good fun though :mrgreen: :lol: :mrgreen:

 

[gas1man]

Hey Stu , following with interest as to what the outcome was of your test drive?

J & P

 

[StuF]

Sorry for the delay in replying guys - completed my test drive without issue!
All working as advertised, pulls strong and clean, shot up the hills around here without any complaints!
Very happy indeed and cant believe the difference in how the bus runs compared to the single carb setup

Have a slightly longer test-drive on Thursday when we leave for DATC15 but fingers crossed all will be well
MOT booked for next week after getting back from Wales and then its off to SPA!

At some point in the future I will probably get the bus on a rolling road and have it tuned properly!

Must have been vibrations from the engine causing airbubbles to get into the fuel system!
Ozzie - I stripped, cleaned and rejetted the carbs before installing them so tried to eliminate any issues that end from the start! 8)