15 replies to this topic

[Scraggydog]

[font=Arial][size=7]
Help,

I have a stock 05 290 fitted the standard Dellorto carb that appears to be fitted in one form or another to most trials bikes.

Occasionally for no apparent reason the bike starts to run very lean at tickover and won't pick up when the throttle is opened. It becomes very diffcult to start. It's as if the air screw adjustment is hugely wrong or the pilot jet is blocked.

As usual, I strip down the carb to it's last componant to find everything clean and unblocked. I blow through every hole with a compressor.

When reassembled it will sometimes work other times it requires another strip down. I have checked all of the jet sizes, the circlip position on the needle and the air screw turns out (3 1/2) against Ryan Young manual. The air filter and box is regularly cleaned.

Does anyone have any suggestions?

Thanks in advance.


Scraggydog

[Alan Bechard]

Does it happen after you wash it normally?

Do you have the vent hoses (or whatever you particularly care to call the things) on the carb?

[HAM2]

Oh, Oh ! This sounds familiar.
There have been a few posts on this subject in the past and they all pointed towards stator trouble( on 04 and 05 bikes).
If the problem worsens when the bike has warmed up then it ''could'' be your stator on the way out.
See previous posts by Andy_290 and Gasgasser.

[titanium]

Did you check the O ring under the plastic cap on top of the carb?

[Howard Wallace]

There is a small o-ring that seals the choke tube into the bottom of the float bowl. Choke tube is the long brass 4mm dia rod and fits into a hole cast into the bowl. The edge of the hole in the bowl needs chamfering as it usually cuts the o-ring, and causes similar problems to that you`ve described. Worth a quick check.
ShercoH

[gasgasssser]

I give you my opinion based on a similar experiance.
If you stator is knackered,either the bike wont run at all,or it will start after being stopped for several hours,then it will run for a short period then give up the ghost again.
Have you assembled your carb correctly?,floats in right way?you havnt blown away the o`ring off the idle screw,or is it the mixture screw?...Sounds like your accelerator cable maybe sticking or binding.Make sure the slide returns to its closed position with a metalic "knock".If you cant hear it,sometings not right.
When you say "runing lean at tickover",do you mean the motor is reving up on its own??,I would say this is a sign that the slide/needle valve is not seating properly,or you have an air leak.

I had an 04 290 with a very similar problem.It would start from cold,although not easily,then it would run for about 10 mins,then cut out dead,no missing or anything to warn me.There was no way it woud start again till several hours later.A new stator sorted it.

Hope you get it sorted.Does your `ead in dunnit???
Steve

[Nigel Dabster]

Floats set at 18.5mm and have you cleaned the filter?

[copemech]

As Al mentioned, the bowl vent lines can certainly cause this.

I have a special vent hose system that I have developed for the Dellorty that utilizes a specially treated ion resistant material which minimizes the surface tension of the fuel bubbles in the lines that can create a vacume in the float chamber yet still prevents water entry. Comes as a kit with the special high flow super fuel supply line!

Edited by copemech, 12 October 2006 - 02:51 AM.

[stump magnet]

definately check the choke tube "O" ring my 06 done the same bought a few new "O" rings and cured the problem

[Scraggydog]

Thanks for all your suggestions, I can strip the carb down blind folded I've done it that many times.

To answer the points in turn.

It doesn't specifically happen after washing though the bike is a pig to start after a wash. If you leave it dry out it starts and runs fine assuming it was running ok before the wash. I do have short vent hoses fitted to stop water getting in a assist blowing out the carb when cleaning.

The failing stator is interesting. I might try measuring the resisitance when the bike is running ok and when it is playing up. Does anyone have any resistances for a Leonelli stator?

I haven't looked at the O ring on top of the carb. Will check this.

The O ring on the choke jet does look like its been chafed where it seats in the float bowl. I'll get this replaced and chamfer the hole.

The slide is seating properly and the cable is correctly routed etc. Its running so lean it won't tick over due to lack of fuel if you give a little choke it it will run at low revs.

The float height is correct and the fuel filter is clean.

Could send some more details of the vent hose system?

I am going to start with the O rings as their the cheapest, knowing my luck it be the stator.

Thanks again, any other suggestions would be appreciated.

Scraggydog

[Alan Bechard]

I would pull the vent lines off, and insure that I cleaned that bottom area of the airbox after each wash before I got into much else.

Actually, I would look at the O-rings just because it would be easy and informational as well.

I have seen where a little water in the bottom of the airbox from washing can drive you nuts trying to figure out what is going on.

[gasgasssser]

hey scraggy,
When your bike is running "ok,"is it exactly how you would expect it to be???,smooth tickover/pickup etc?

Steve

PS when you say its running lean,how do you know this?,what are the symptoms

Edited by gasgasssser, 12 October 2006 - 09:28 PM.

[copemech]

Could not get a nibble! Oh well!

[Neil King]

Scraggydog, on Oct 11 2006, 05:37 AM, said:

[font=Arial][size=7]
Help,

I have a stock 05 290 fitted the standard Dellorto carb that appears to be fitted in one form or another to most trials bikes.

Occasionally for no apparent reason the bike starts to run very lean at tickover and won't pick up when the throttle is opened. It becomes very diffcult to start. It's as if the air screw adjustment is hugely wrong or the pilot jet is blocked.

As usual, I strip down the carb to it's last componant to find everything clean and unblocked. I blow through every hole with a compressor.

When reassembled it will sometimes work other times it requires another strip down. I have checked all of the jet sizes, the circlip position on the needle and the air screw turns out (3 1/2) against Ryan Young manual. The air filter and box is regularly cleaned.

Does anyone have any suggestions?

Thanks in advance.


Scraggydog

Sd, my 2000 montesa is doing the same thing. I am pretty sure the pilot jet is clogging up. Last night, instead of removing the carb again, I removed the pilot screw and blew compressed air into the hole and that cured it. The last time I actually drilled the pilot to a larger size. That helped a lot, but then when I went to ride it yesterday it was running like crap again. Mine starts surging and I keep screwing in the air screw till its screwed in all the way. Then sometimes it won't start till I choke it. I'm wandering if there is not a screen in the fuel tank and I need to put a filter on the fuel line. I've only had this bike about a month and am new to trials, but the bike is very hard to control when it starts running like that.

[gasgasssser]

Hi`
you`v obviously got one or two problems there,but at the end of the day,you shouldnt have to keep messing with the air screw and mixture etc.Every body always goes for the carb,but carbs are relativley problem free and usually the problems lie elswhwhere,i know this from my own experiances.You say you are new,my advice is make sure you have the correct pilot and main jets,and the correct fuel.There is no way you should be drilling jets out bigger.Clean carb thoroughly,use compressed air if available.Make sure needle valve clip is in correct poition.Also,get an exploded drawing of your carb to make sure nothing is missing
Check carb for any obviouse faults such as fuel leaks,cracks in carb body etc.
If it doesnt run now,chances are someting else is causing the problem.

Steve