115, 1989 CELTO stalling at idle

[Wakeboard in North Wales]

We have been running the above yammy V4 with an intermittent yearly problem. We can start the motor with enegine choke on, and warm start. We then close the engine choke, and the engine revs freely with the warm start lever fully up. As soon as we try to reduce the warm start to idle the ending stalls.

The engine is powered by an inboard tank, which has been pumped out twice. The engine has been serviced, new plugs, filter and impellor.

Tonight we managed to get the engine started, and once we managed to get it in gear (without stalling the engine revved fine at 5500 rpm and the boat did 45mph). As soon as the revs drop to 3000rpm the engine starts to struggle (and almost misfires). At low revs we can hear an almost hissing noise coming from the engine.

To try and get the engine started we cleaned the idle jets on the top carb, and they were clogged with an oily residue (did not have time to do the lower card).

I am hoping that the bottom bank of carbs need to have the idle jets cleared, as once the engine gets above 3000 rpm it runs fine.

Any tips re: other causes, or how to effectively clean carbs etc etc.

[Ken]

Wakeboard,
You need to remove all carbs, teardown, clean, and install carb kits. Check all jets - for those that have o-rings that are cracked or distorted, replace the o-rings.
A good carb cleaner is Berryman's Chemtool.
Good luck [img]smile.gif[/img] ,
Ken K

[Wakeboard in North Wales]

I'll order the kits, in the meantime someone mentioned a quick fix is to fill in the inline fuel resevoir with carb cleaner, and then fire the motor. In theory it should clear anything lying behind the jets. That is plan A and then I'll revert ot plan B (the carb rebuild). Will post the results. What is irritating was that I asked the boat mech as part of the service to clean the carb's, he obviously did not touch them.

[Gary Price]

Hi,
I am in North Wales (Ewloe, Flintshire). I have a 130hp V4. Having a few probs myself a the moment (See posts on thermostats and oil overflow). Drop me line garyprice@totalise.co.uk

[Ken]

Wakeboard,
You can do a shock treatment with a strong detergent like Seafoam or Yamaha RingFree - this will de-carbonize the rings and pistons, and clean up the fuel system somewhat, but it is not a cure-all for carbs that are clogged up with gum/varnish.
For carbs that are mildly clogged up, then a shock treatment works sometimes. You really need to be using a detergent on a regular basis when dealing with a 2-stroke engine because of the carbon builup. That's why Yamaha recommends you use their "RingFree" all the time, but I think that is an overkill. I use Seafoam, 16 oz to 16 gallon of gas, approximately every third sixteeen gallons. You will get varying opinions on this. If you use a detergent on a regular basis, then you will keep carbon builup at a minimum and also keep the fuel system relatively clean.
There are also different ways to do a shock treatment. I prefer to mix 16 oz can of Seafoam to 3/4 gal of gas and 3(2 if oil injected) oz of oil in small container (see my post to "CLL" dated May 27, 2005). Another way is to fill the remote in-line fuel filter/water separator with pure Seafoam - but you don't want to do this if you have a pre-mix like mine for obvious reasons.
Good luck, and let us know how you come out with the carbs [img]smile.gif[/img] .
Ken K

[Wakeboard in North Wales]

Thanks for the tip, we cannot get seafoam in the UK, so I going to go with car carb cleaner, and fill the inline filter (as plan A), followed by a strip-down, and then a rebuild if needed....

[Gary Price]

You mentioned in your original post that you can hear a "hissing noise" that could indicate an air leak on the carbs. An air leak would create a weak mixture - more noticable at low revs. Have you checked for any loose or missing pipes, carb to manifold gaskets, etc.

[Wakeboard in North Wales]

Well we have done some more detective work today:

Filled the inline fuel filter with Carb Cleaner (Ken's deep shock), and also sprayed the cleaner into the air intake. It again ran well over 3000 rpm but below it faltered and stalled.

Next we removed each carb, and cleaned all jets, and there was a degree of congealed muck in each carb.

We rebuilt the carbs (no mean feat when the boat is on the water in a marina).

Anyway restarted it and no improvement, although interestingly as a test, when the engine sounds like it is going to stall, if I turn on the engine choke, it improves.

We can still hear the hissing sound, so I think it must either be an air leak somewhere (although not obvious as the hoses seem to work ok), or a fuel pump problem, as I think we have ruled out the carb's...

Anyone out there have any other ideas please chip in.

[jb123]

If choking, enrichening, the mix helps, the carbs need to be gone thru again.use a spray bottle with gas in it and spray in each throat and you will find your culprit.or, put your finger in each throat, one at a time, simulating choking for the same result.check the pumps by blowing thru them, upwards should allow passage, opposite should not allow ANY.

[Ken]

Wakeboard,
Since your motor runs fine at high speed, I think your fuel pump is ok. Sounds like the low speed jets of the carbs are still plugged up. I would tear the carbs down and let them soak over night - clean out all passages. Also, replace all gaskets and seals that should have come with the carb kit.
Good luck and lets us know how you come out,
Ken K [img]smile.gif[/img]

[Wakeboard in North Wales]

Well a bit more progress. This week I took the carbs off the boat, and soaked the bottom of the carb in thinners. I then used a high pressure jet to remove anything left behind, and the carb/jets are spotless.

Next I stipped the fuel pump and this is fine.

I started the motor up and above 3000 revs the engine seemed to run a little more stable, although it still stalls at idle.

I then took one plug cap off (the lower right cylinder) whilst the engine was running at approx 2500 revs and there was no deterioration in engine performance. Next I took the plug out and attached it to the cap and left resting against the engine case, there is a spark and the engine started.

I performed the same task on the lower right cylinder and exactly the same thing happened (no deterioration). It therefore sounds like that at revs under approx 2500 the engine fires only on 2 cylinders (top bank).

I then remembered on the way home, that when I serviced the carbs I removed the idle adjustment screws at the top left/right of each carb, and may have overtightened each screw, and not returned it to the same position (this applies only to the lower carb which services the lower 2 cylinders). Could this in theory then (overtightened idle adjustment screw on lower carbs) cause a motor to stall at low revs due to it running on only 2 cylinders?

The only other thing I can think it is, is bad fuel (although surely it would not run ok at high revs, and tank was cleaned at the beginning of the season), or perhaps faulty end caps (plug), coil/cdi unit?

Any help gratefully received?

[Wakeboard in North Wales]

Another update:

Changed the slow idle adjustment on both carb's and whilst it did make a change, the engine still runs rough. I can start the engine with warm start (half lever), and the engine revs up to 2000 (takes a while), and then if I give it more juice it will rev right up to 4500. At 4500 I removed one plug lead on lower left cylinder, and no noticeable difference. As soon as I go below 2000 it stalls. I cannot start the motor without choke (even once warm), and it always stalls before I select neutral...

I removed the plug lead from the top left cylinder and the plug lead fell out of the coil. Should they do this? Do I just screw it back in or do I need a new coil. All plug caps are rusted, will replace tommorrow.

All plugs are black (which indicates fuel is getting through). Is my problem fuel related (as the bottom 2 cylinders are the ones which seem to be misfiring, which are fed by the bottom carb), or ignition or cylinder compression (I have sort of ruled this out, as 2 cyl's do not work).

[Wakeboard in North Wales]

Well the boat is fixed. Stripped the carbs again and, on suggestion from an engineer friend, looked at the bottom carb idle speed adjustment screw.

Underneath the screw are 4 small holes. When the butterfly valve is shut only the first hole is left exposed on the engine side of the carb. Both the left/right carbs had the first hole blocked with swarf. Cleaned the swarf out, put the carbs on and it runs like a dream.

Sometimes the engine stalls and almost backfires, by my guess this may be due to the engine sitting low in the water and the exhaust ports sometimes sucking in water.

Thanks for the help....

[jb123]

synching carbs and readjusting your air screws should fix your idle issue.

[Wakeboard in North Wales]

Ho do I syc carbs?

Do u mean the idle adjust screws or the one idle screw which touches the throttle cam?