carburation issues.

Maestro, SEI-V
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bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

carburation issues.

Post by bigred »

Hi just got over 100 miles on the bike from the recommisioning. I set the carbs up and it ticks over very well. I used gauges to set the throttle balancing coming off idle but im getting rough running coming on and off idle posision. Also getting 8 stroking at low throttle when bimbling through town. It all clears up nicely from 1/8 / 1/4 throttle up. I dont think its the chokes as its ticking over very well. when rolling off throttle im getting a bit of popping from the exhausts.
Ive refurbished the carbs with new o rings and gaskets etc.
Any suggestion of what to look for or adjustment tweeks would be gratefully recieved.
MickeyMoto
Posts: 2415
Joined: 22 Nov 2008 17:41
Location: Even further oop North

Re: carburation issues.

Post by MickeyMoto »

What size pilot jet are you running?
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

Hi. Spent too much time finding out its a cable issue. I replaced the choke cables during rebuild but thought the accelerator cables would do until winter. However the front carbs cable is now not allowing the slide to drop fully down to the adjuster screw. So im getting partial throttle on the front cylinder all the time. New cables on order from Medina italia. Hopefuly I can reset the carbs up and all wil be well. It was running so well :cry:
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: carburation issues.

Post by 3potjohn »

Control cables can be such a nuisance. The outers seem to stretch or the inners fray. Sometimes on full lock it pulls on a carb. When you get them make a note of the measurement of the inner, nipple dimensions, the outer including ferrule length and the widths.
Then at some future stage you can make up your own.
I have done this for my throttle and clutch cables.
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

New cables fitted today. Plenty of adjustment and the slides drop fully down. I am using Davida gauges to balance the carbs. At the moment its very difficult to get it to balence at idle. and even worse as the throttle comes off idle.
I started with 1 1/2 turns out for the idle screw but I can screw the front carb idle screw all the way in and it gets faster! That suggests it running rich?
Im wondering if the floats are at the wrong height. Something I didnt check. If they are too high it can richen the main jet up.
The chokes are sitting fully down when off but I didnt replace the rubber insets in the bottom of the choke plunger and they did have a slight circular ridge in them.
Ive got plenty of experience with Amal carbs but not dellotos.
Any suggestions would be gratefully received
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

the float height is 24mm which appears to be spot on. Everything looks good except the choke rubber. I will order some replacements and see if that stops the rich idle.
Attachments
choke rubber.jpg
choke rubber.jpg (295.01 KiB) Viewed 4817 times
norbert
Posts: 750
Joined: 15 May 2007 15:15
Location: Lübeck/Germany

Re: carburation issues.

Post by norbert »

And have a look at the little mixture screws. Especially the fron one may have lost the peak. There schould be the srew with its peak, the spring, a little washer and at least a small O-ring. the washer is to protect the O-ring towards the spring.
Emmohaswheelsagain
Posts: 358
Joined: 28 Jun 2008 21:13
Location: Lincolnshire

Re: carburation issues.

Post by Emmohaswheelsagain »

It would be worth changing the chokes, are you using the standard cable chokes?
My 500 was running rich, front cylinder only, so I ditched the standard cable chokes and replaced with the flick up chokes.
These are a straight fit on the carbs and at the same time give you more room under the tank for the routing of the throttle cables.
Regarding the mixture screws it is not unusual for the bike to run best at different settings. I have cleaned and rebuilt my carbs with new gaskets, needles and float pins, presently the settings on the mixture screws are 2 1/2 front and 1 3/4 rear, it starts well, is balanced at idle and is reasonably close to balanced when opening the throttle. I will probably tweak these settings once I have ridden the bike a few times. I am sure the age of the bike and the wear on the throttle bodies is a determining factor here so it may be practical to accept that your outcome as the best you can achieve. I am going to do a compression test, I previously owned a 500 in the 80’s which did suffer from a burnt out exhaust valve. These bikes come to us with a limited amount of history, mine has had 9 previous owners of which I have only documentation relating to two. I trust you will get there in the end, I suppose it is a matter of enjoying the process, at least that is what I say to myself when ordering another part.
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: carburation issues.

Post by 3potjohn »

I had mixture screw issues recently on PHBH28BS carbs. New o rings and washers. One side responded correctly, with the motor slowing as the screw closed. Optimum about 1.5 turns out.
The other side caused increasing RPM as it screwed all the way in.
Float height checked,float type now black, was previously white. Fuel volume in bowls about the same given a bit of spillage.
I have slack in the cable chokes and even replaced one cable choke with a new flip up type to test.No change.
Removing both mixture screws, blasting through with carb cleaner, then swapping the screws gave an improvement.
I called it a day and immediately went to Nerja.
Will double check next week.
John
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

The issues continue. Fitted the new rubbers to the choke plungers ( not an easy job) and the engine ran like a pig. Now no gauge reading at all on front cylinder. The rubber manifold had split. :( . Ive ordered two new manifolds and two flip choke assemblies from medina. My wife will cut up my credit card at this rate. Hopefully this will solve the carburation issues. :roll:
Ive ordered the 34mm choke assemblies but there is a 42mm version. Is the 34mm ok?
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: carburation issues.

Post by 3potjohn »

The 34 mm is right. Do not let her cut up your card until after you need to order anything from Startgomma!
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

Bits all arrived from medina and fitted ok including the flip top chokes. Amazing! balanced so easily. Idle jet adjustment very easy and roughly the same each side. Adjusted the throttle cables so balanced transition from idle to higher revs. I noticed the idle mixture screw plays an important part in the transition from idle to part throttle. Had to adjust each carbs idle mixture to get the transition smooth. Generally I had to adjust the screw futher out on both to remove hesitation during the transition.

Very smooth now and the bike sounds so much better. I must have had a air leak through the rubber manifold from the beginning. Just got to go for a ride soon but waiting for new jubilee clips to arrive for the mainfolds.
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

following fitting the inlet manifold clamp rings the bike is much better but now I'm getting poor throttle action from idle to take up. Can anyone tell me the correct slide for my bike? I think it might be due to the cutaway.
cheers
bigred
Posts: 64
Joined: 05 Dec 2022 19:19
Location: swindon england

Re: carburation issues.

Post by bigred »

Posting this for reference for other sufferers.
The carbs were causing backfire and it did it during an electric start. The resulting backfire ripped the electric start chain apart which then ripped through the side cover and also broke the mounting lugs of the motor! :shock:
I fitted plastic clamps sourced from medina over the rubber manifolds at the inlet end and that has stopped the air leaks at last. :D
Also found it was running far too rich at tickover and the previous owner had fitted bigger idle jets so replaced those with stock and using kick start got everything running and balenced :wink: No backfires at all now.
Sourced a new starter cover from Germany which had a great starter clutch spigot and got the lugs aluminium welded back on the starter motor.
Shimmed up everything and chain waxed the new starter chain and both sprockets. Assembled it all into the case and case to the engine. Starter ran great. Phew!
Petrol in the engine and had to use the chokes to get the bike to start. A first since I have had the bike. Its all running great.
I have got 200 miles on the bike since the recommision months ago and I am hoping to get out to local bike meets and to the classic motor hub biburys big bike meet in july.
In all honesty this bike has been a pain in the axse and a pain in my wallet. I am just hoping for a few pain free miles now.
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