Suzuki DT25 Idle Problems

al40 · 11 November 2006, 15:25

Hi,

Got a Suzuki 25 Oil injection 2-stroke which I have just put back on the boat after removing it Jan this year. It wouldn't start at first so I stripped down the carbs etc, cleaned them all out (they were full of muck), replaced the plugs and it now starts well and runs at fast idle but does not run at normal tickover speed. No idea of actual rev's but when it's throttled back down from fast it dies. I can get it to idle by kicking the choke every 5 seconds or so by pushing in the key briefly). Similarly, when it's put into gear, it dies unless I toggle the choke until the rev's are up to I'm guessing 2500, then it seems to run fine.

The carbs are clean to the best of my knowledge but I accept they still may be dirt in the jets.

After taking the engine apart, I am running it pre-mix (not sure of ration, I just glugged some oil into fuel, but it's prob approx 50:1) just in case any air bubbles got into the oil injection system. I would not have thought this would make any diff.

Have tried adjusting the mixture but didn't seem to help. I set them at a base of 2.5 turns out and tried 3 and also 2.

Anyone any thoughts? It screams out as a mixture / carb thing to me because of the way it behaves when choked but I just can't see the problem... Could this be a carb balance issue?

Thanks,
Al.

Nos4r2 · 11 November 2006, 16:33

Idle jets are probably blocked-blow them through with an airline.

A carb clean is more involved than most people think.

al40 · 11 November 2006, 18:53

Quote:

Originally Posted by Nos4r2

A carb clean is more involved than most people think.

I stripped them all down, removing all jets and nozzles etc, reset float level, checked float was actually operating valve OK. Done this many times before on other engines and previously been able to fix the problem. What else is there to it?

I did blow the jets out by mouth and then washed carb out with fuel to remove any moisture and they seemed to be OK in that fuel could pass through the jet passages as far as I could tell - I don't have access to an airline and have found the small cans of compressed air (air duster) to be useless.

Nos4r2 · 11 November 2006, 22:54

You sound like you've done a pretty good job on it. It doesn't take much to block an idle jet though.

What settings does the manual say for the airscrew? I'd try 1-1.5 turns then 3.5-4.5 turns. Those are the 2 settings that from memory Suzuki bike carbs use.

Like you said, it could well be balancing too. Do you have a set of vacuum gauges (and does it have a gauge takeoff)?

al40 · 12 November 2006, 21:09

Agreed, it could still be the idle jets (and probably is). From memory, the clymer manual says 2.5 turns. No unfortunately I don't have any vaccum guages. I have balanced the carbs by eye so the plates all start to move at same time but I know that's not very scientific!

I guess I need to find someone with a good compressed air hose!

Thanks,
Al

Nos4r2 · 12 November 2006, 21:21

You haven't accidentally undone the cable adjustment by a turn or so have you?

If you can find a garage with a proper airline rather than the new digital ones it'll do the trick too-just make a nozzle out of an old tyre valve.

al40 · 13 November 2006, 21:57

Quote:

Originally Posted by Nos4r2

You haven't accidentally undone the cable adjustment by a turn or so have you?

If you can find a garage with a proper airline rather than the new digital ones it'll do the trick too-just make a nozzle out of an old tyre valve.

By cable adjustment do you mean the link arm between all 3 carbs? If so, no I haven't altered that.

Air hose at a garage - good suggestion! I think my local garage does have digital one but you can put it on the "flat" setting and it'll still work OK (I think it's still got an accumulator tank so there is actuall compressed air rather than just a pump)

Nos4r2 · 14 November 2006, 03:00

Quote:

Originally Posted by al40

By cable adjustment do you mean the link arm between all 3 carbs? If so, no I haven't altered that.

No, the screw thread on the end of the cable itself where it goes into the motor or the controls.

al40 · 14 November 2006, 16:23

I re-installed the engine so yes, the cables have been altered, however the cables are not tensioned at idle (ie throttle on carbs sit at idle stop as far as I can tell). I don't think would have a huge impact on not running at idle? as it doesn't "idle" till rev's are pretty high. It's not like it's dying due to running just a little bit too slow. The speed it will run at (fast idle) is fast enough that I certainly wouldn't want to put it into gear at those rev's - I'm guessing 2500rpm.

IBWET · 14 November 2006, 17:58

Al,

If you can remove the jets at the marina this weekend, I know someone with an airline..it's a regular occurance with me.. once a year with the malta.

Other thing that sprang to mind a bit more concerning, is it sucking air from somewhere it should'nt? weakening the mixture so low at idle, it stops?.

al40 · 15 November 2006, 19:02

IBWET,

Thanks for the offer! Engine is currently in my garage but I may be down at marina this weekend - if so I'll take the carbs off and give you a shout

Cheers,
Al

Nos4r2 · 15 November 2006, 22:45

Quote:

Originally Posted by al40

I re-installed the engine so yes, the cables have been altered, however the cables are not tensioned at idle (ie throttle on carbs sit at idle stop as far as I can tell). I don't think would have a huge impact on not running at idle? as it doesn't "idle" till rev's are pretty high. It's not like it's dying due to running just a little bit too slow. The speed it will run at (fast idle) is fast enough that I certainly wouldn't want to put it into gear at those rev's - I'm guessing 2500rpm.

That doesn't sound like jets. Idle jet is pretty much redundant past 1500 rpm.

al40 · 15 November 2006, 22:58

It certainly seems to run fine after a certain throttle point. I was assuming idle jets because of this (and the fact it won't idle without choke). No idea of actual rev's but I'm guessing RIB is doing 4-5knts at the point it will actually run.

Nos4r2 · 15 November 2006, 23:04

I think IBWET's air leak theory may hold some water

al40 · 16 November 2006, 23:22

Quote:

Originally Posted by Nos4r2

I think IBWET's air leak theory may hold some water

Yes possibly. If it's an air leak, 1st place to suspect is the gasket right? The gaskets are quite thick and pliable but it may be time they were replaced. I didn't replace them when I cleaned the carbs

Nos4r2 · 17 November 2006, 05:10

Quote:

Originally Posted by al40

Yes possibly. If it's an air leak, 1st place to suspect is the gasket right? The gaskets are quite thick and pliable but it may be time they were replaced. I didn't replace them when I cleaned the carbs

Fire it up and spray wd40 at anywhere you suspect of an air leak. If it's leaking the revs will rise when you spray in the right place.

al40 · 17 November 2006, 22:16

Good idea! Boat is currently in my garage so I guess it'll have to wait until I tow it to somewhere with some water - don't fancy running it with muffs in my garage!

neb · 18 November 2006, 07:46

Quote:

Originally Posted by Nos4r2

Fire it up and spray wd40 at anywhere you suspect of an air leak. If it's leaking the revs will rise when you spray in the right place.

Be very careful doing this as WD40 is flammable - I once fried a motorbike doing exactly this.

Nos4r2 · 18 November 2006, 09:53

Quote:

Originally Posted by neb

Be very careful doing this as WD40 is flammable - I once fried a motorbike doing exactly this.

It's safe enough as long as the carbs aren't spitting back-don't do it if they are. The coils and plug leads are far enough away from the carbs not to cause a problem. Use the tube on the wd40.

ADS · 18 November 2006, 15:07

If its not the carbs check your fuel hose between the engine and the tank + the primer bulb, any split in that will suck in some air.