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Carburation on DR600

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Hi,

I have spent a lot of time on this but always seem to be chasing something. First of all, the information required:

1) Suzuki DR600 1985.

2) Typical UK weather. I dont know elevation but it's not particularly high.

3) Exhaust is pretty free flowing, air box has been modified for better flow, some basic tidying up in the ports (nothing extreme).

4) Currently I have a 142.5 main and a 25 pilot. Believe the clip is in middle. Needle and emulsifying tube are new. Dont know needle taper. (stock jets are 135 and 20).

5) Off Idle stall or miss. Not every time but usually stumbles. Better if throttle used gently. I am happy with the main jet and the needle. Today I checked the float level with some plastic tube although I was happy with the physical setting. The manual is really unclear about the fuel level, I believe the level should be 3.5mm below the join (it could be above, the picture is rubbish) but it was about 2mm above. I adjusted it so it was just below the join and went for a ride.

With the stumble as good as gone and bike pulling nicer than it ever has, I thought it was cured but the idle was now hanging and bike kept stalling from idle. This was with a 22.5 pilot. I went up to 25 and still could not get a good idle so I raised the float level slightly.

Now I have a bike that still pulls quite nicely, idles perfectly (though the screw is probably out 3-4 turns so not ideal) and the off idle problem is back. However it isn't so bad but it's certainly not right - blipping the throttle will probably stall the engine. I don't know what to do next. If I keep the low float level I would need at least a 27.5 pilot which is getting rather big, but then I can't run properly on a main smaller than 142.5, so maybe that is exactly what I need to do?

Also, before I lowered the float, riding at low rev's and small throttle openings was really lumpy, now it's pretty smooth.

I find it very hard to tell, but I think there is a very slight surge when coming from WOT to about 3/4. Could this mean that the float change has effected the needle and I should raise it another clip (quite a task on my bike)? I was pretty happy that I had ironed it out before today.

It is the mikuni slide carb - I think its a VM40.

I will have to buy more jets if going above 25 but I would like to know if I am missing something before I buy more.

The bike is only used on road. I hope there is enough detail here as I have been doing this over time - when I get the time so some of it is a bit fuzzy.

I would very much appreciate some help!

Thanks.

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Thanks Krannie, I will try that. I assume the lower float level has caused the needle to be leaner then?

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OK, so I finally got a chance to play with the needle.

The clip was 1 notch to the lean side of middle.I moved it 2 slots richer hoping for an obvious difference. It hasn't done anything I can notice. I was unable to ride it as p*ssing down with rain and only had my dinner hour but I'm sure there is no change.

I know moving the clip does effect the engine, previously if I moved it leaner it would pop like hell all the time.

So to clarify exactly what happens, crank it open and it usually stalls. Sometimes it gives out a bang and flounders a bit and never seems to rev up, just kind of sticks, and others it revs up nicely.

I also noticed an ever so slight hang before returning to idle.

I tried holding the throttle off idle and a little above that and it wont hold constant revs (it's not reciculous but definately not right). You can hear some miss-fires as well.

I sprayed WD40 all over the carb with it idling and nothing changed at all. The idle is still really good BTW. As always, dead easy to start - second kick.

I have 1 slot left on the needle which would be the richest setting, it is quite a task to move it so unless advised it will achieve something, I won't bother...

Pretty fed up with this now so as always, help greatly appreciated!

Kevin.

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hi, did u ever sort this problem out mate?

got similar issues, just completely rebuilt accelerator pumps and hoping

bbut whats the deal with float height? manual figures seem totally wrong, saying 25mm from base flange to top of float

but upside down resting on needle its 71mm, and pushed as far into carb as possible its still 56mm so the 23mm cant be right

any hints anyone? know its an old thread but heres hoping :-) cheers in advance

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4 hours ago, earthcore said:

hi, did u ever sort this problem out mate?

got similar issues, just completely rebuilt accelerator pumps and hoping

bbut whats the deal with float height? manual figures seem totally wrong, saying 25mm from base flange to top of float

but upside down resting on needle its 71mm, and pushed as far into carb as possible its still 56mm so the 23mm cant be right

any hints anyone? know its an old thread but heres hoping :-) cheers in advance

I havent seen a carburetor that had a measurement of 71mm from the surface that the float bowl mates to,  to the extreme side of the float lobes.  

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know what u mean mate, but like i say, even with float pushed right up on pivot, without needle in at all, its still over 55mm from flange to base of floats

so the 70mm leaves a max float travel of 20mm which sounds fairly near

when its on ill check level with an external pipe but as stated above its not very clear in manual about where the measurement is taken from

and crannie, what makes you say that?

intake shows no sign of wear and float needle seats well and shows no distortion/wear

 

Edited by earthcore

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well fuelling finally sort of sorted,

tickover fine, and when i got the fuelling at the top end right it just pulled the clutch plates apart

so rebuilding clutch now before i do a final shakedown

but the lack of engine braking is still an issue, just makes no sense to me

and i do still have to turn the tickover lower when it gets hotter too

anyone else have this issue?

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