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RSRBOB, Technician
Category: Motorcycle
Satisfied Customers: 1078
Experience:  Former Factory Service Rep, Dlr Line Tech, Service Manager, General Manager, Store Owner
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I will give this a try as this is the 2nd unit with this

Customer Question

I will give this a try as this is the 2nd unit with this problem
JA: What is the model/year of your motorcycle?
Customer: 2002 suz 250 ozark
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: the problem is with the idle. 1) found that that vac petcock was leaking fuel on the vac line. This caused rick condition. replaced petcock, fuel line and fuel. Start unit and it idles at a high rpm, adjust idle speed screw down, idle will start to decrease and then unit will shut off. will restart with full throttle appears to be slightly flooded. Removed and checked carb, disassembled and cleaned (not really dirty) reinstalled and have same problem. adjust pilot fuel screw in and it picks up some rpm but will run with the screw closed off.
JA: Just to clarify, can you actually see the leak?
Customer: the fuel leak in the vac line, yes because fuel would run out of the hose when disconnected
JA: Anything else you think the mechanic should know?
Customer: not at this time
Submitted: 2 months ago.
Category: Motorcycle
Expert:  RSRBOB replied 2 months ago.

Hi and thank you for your question.

Just to clarify, when you replaced the petcock, it solved the problem of the fuel leak?

Now, the engine will not idle down?


Customer: replied 2 months ago.
the fuel leaking into the vac line is fixed. Now there is a second problem. Unit starts fine but has high idle for 30 -40 sec then come to a normal idle speed for a short period of time and then just dies. It sounds like is getting rich. Choke is off and not leaking. Will restart but is slightly flooded. Adjust pilot fuel screw in (leaner) rpm does lean some but can close screw it will still idle with the same results. All jetting is stock. Float is set @15mm.
Expert:  RSRBOB replied 2 months ago.

Thank you for the additional information.

I suggest trying a test. Use a can of contact cleaner and spray the intake area between the carb and cylinder head, while the engine is running. What you are listening for is any change in engine RPM.

Customer: replied 2 months ago.
I did this looking for any leaks, found non. Have tried with air filter removed, no difference. Carb appears to have a spring/vac accelerator pump which I have not seen before. I believe vac keeps it closed and when throttle is opened vac drops and the spring pushes against diaghram to open and allow some fuel to flow to main jet and as vac increases it close again. Also spark plug is dry black sooty which means fuel rich?
Expert:  RSRBOB replied 2 months ago.

Have you by chance checked the valve clearance lately? Tight valves can create some erratic idle issues as well. The component you are describing is not an accelerator pump. It is called either an air cut valve or a coasting enrichener. The purpose of it is to cut off the air jet passage to the idle jet when the throttle is chopped at high RPMS. When that happens, the mixture goes very lean and causes after fire in the pipes. By cutting off the air from the idle air jet, the high engine vacuum draws only fuel from the idle jet, making it richer. Rich enough to actually burn in the combustion chamber, instead of being so lean raw gas passes straight through, accumulating in the pipe and igniting when a sufficient amount gathers to support combustion, creating that nasty after fire, either popping or sometimes a bang out the exhaust. It would not have anything to do with the symptoms you are describing.

Customer: replied 2 months ago.
Thanks for the explaination I understand the purpose. No have not checked the valve clearance yet, I will be doing that 1st thing in the morning. Do you know the spec?
Expert:  RSRBOB replied 2 months ago.

Int - .03-.08mm, .001-.003", Ex - .08 - .13mm, .003" - .005"

Customer: replied 2 months ago.
I check the valve settings , intake was .06 reset to .03, ex was .09 reset to .051st start (cold) idled fine could adjust pilot fuel screw in rpm up, out rpm down (rich) set in middle. Rode, eng now hot idle high then comes down and sound is rich eng dies. Restart throttle full open and it repeats high down normal dies.
Check charge voltage @ battery reads 14.98 volts.
Customer: replied 2 months ago.
Should clarify the valve setting.
Intake .006" set to.003"
Exh .009" set to .005"Are there any specs for peak voltage of the ign system?
Expert:  RSRBOB replied 2 months ago.

As far as adjusting fuel mixture screw, you should set it to the highest possible idle RPM, then richen it up so you have max idle RPM minus 50 rpm. So that is just a sliver on the rich side of perfect. Splitting the difference is definitely going to be rich. The other point you just made was it runs better cold than hot. This is also an indicator that it is running rich. An engine richens up as it warms up. Have you checked the float level and made sure it wasn't set too high?

If the valves were not too tight, they won't affect idle RPM either. The other point you made was running this with the A/F out does not make a difference. It should be way too lean with no A/F. Can you actually rev and ride the ATV with no A/F? It seriously should not be rideable without an A/F.

Now I am curious how long this problem has existed, and what other history you have with this unit? I feel like I need to know more details now. Did this happen all of a sudden, or gradually got worse, or was it ok the last time you rode it, and then it never ran right the next time you took out, and ever since? What?


I am sure there are specs for the ignition but an ignition isnt going to give you a high idle, unless it is mysteriously advancing the ignition by itself, which all you need to check that is a timing light. Compare timing at cold start up to timing when warmed up.

Customer: replied 2 months ago.
1) ran OK before, complaint was will not idle, found fuel in petcock vac line, eng running rich, replaced petcock, started eng everything working correctly, eng warms up will not idle, tried adjusting pilot fuel screw to no effect. Removed carb, disassembled and cleaned, inspected all parts for any damage found not. Check all jet sizes to specs OK. Measured float level, measured @15mm spec number I had was 12-18mm. With no a/f yes I know it should be lean as that is the reason I tried it removed. Effect was no help @idle and lean when riding. No problems when riding till you want to idle and it sounds rich and dies. (a/f installed or not) I may be missing something but after 40 years experience I am at a dead end that is the reason for this conversation
I hope I have explained what has gone on since I started working on this unit
Expert:  RSRBOB replied 2 months ago.

So above idle it runs fine, but once warmed up, it sounds rich at idle. Does it smell rich too?

This leads me to believe either the PJ is too big, no matter what the # on the side says, or, the carb body is damaged where the fuel screw enters the venturi from someone forcing the screw in too far.

I would order a new stock PJ and install that and re-test. It sounds like it may have gotten enlarged at some point causing it to be larger internally than what the size indicated. At this point, it is indicated and relatively inexpensive to replace.

At 15mm float height is the float arm about parallel to the float bowl gasket surface? 40 years experience doing what, out of curiosity?

Customer: replied 2 months ago.
I have thought about pilot jet but did not have 1 small enough (17.5) will get one.Grew up around lawn & garden business which in later years became a snowmobile, motorcycle dealer. Degree in mech design. 15 years retail and service of Snowmobile, motorcycle, small eng.
25 years with manufacture in R and D and testing and production calibration.Like I said in the beginning this is the 2nd one I have had that has the same running problem with a couple of twist. The 1st unit has a new production carb. Both have me stumped and this why we are having the conversation to try to put another brain to it. Sorry if any miss spells because my phone @ time likes to change words.
We will continue conversation as we go forward. Thanks
Expert:  RSRBOB replied 2 months ago.

Super.Sounds good. Which manufacturer were you with? I can live with the words. Trust me, auto correct does me in quite often.

Expert:  RSRBOB replied 2 months ago.

I have a couple of more suggestions, or questions to enter in to the equation.

First, did you check the pilot air jet that is under the diaphragm slide? It is a 170 so it had a huge hole in it but worth checking it out.

Next, could there either be debris under the enrichener plunger holding it open or perhaps the rubber seal on the business end of that same plunger is either cracked or missing, causing it to run rich because the enrichener is leaking?

Customer: replied 2 months ago.
Pilot air jet has very large hole, I looked at the number but do not have my notes with me @this time.
Checked choke plunger for damage. Rubber seat is intact, not deteriorated from age with a good seal area.
Inspected carb body @ seal area for any pitting or corrosion of the aluminium body from poor fuels etc. Non found. Cable free play is more than enough with no binding or sticking.
Today I found a pilot jet, but a couple of sizes smaller, will try and see what happens. ( next week sometime).
As I had another Suz 250 with the same problem just took longer running time to act up and this unit had a complete new carb assy.I retired from Yamaha in 2009 after 25 yrs.
I did some contact work for Arctic Cat with there side by sides and there Snowmobiles and Camoplast with there track systems.
For the past couple of years I been working part time for a small repair shop in town, for the most part I get the problem child's to figure out. For the most part goes good, but every now and then get stumped even for a old far!!!.
I should say I am not a part replacer with out a reason and a test to say why, this comes background but sometime you have to break from habit, so I try.
Will keep in touch with some results as we move forward.
Expert:  RSRBOB replied 2 months ago.

Were you in the motorsports div? If so, we know each other. Recognize the initials before my name?

Expert:  RSRBOB replied 2 months ago.

BTW, I did mention the huge hole in the PAJ..

Also, I was in the SE, where were you? I left in 2000 after 8 years.

Customer: replied 2 months ago.
Small world. I was in motorsports div.
I was in the coon rapids r&d 1st back in 1986. There our job or direction was always changing. In about 1992 or so I moved over to testing but with snowmobiles only. In 2000 Yam sold the MN facility and engineering moved to Minocqua Wi. We mostly likely have meet @ sometime along the way.
This is becoming more interesting as time goes. Later and have a good weekend.Thanks
Expert:  RSRBOB replied 2 months ago.

Yw. Being in the SE, we didn't have much to do with SMB. So you probably spent more time with Robert P, Joe P and the guys from Cudahy. My buddy and I volunteered to do some testing on SMB one time when they needed help but we didn't get picked. Never rode a SMB, maybe someday.

Expert:  RSRBOB replied 2 months ago.


Have you made any more headway on this?

Customer: replied 2 months ago.
Hi Bob,
Sorry it has been awhile. Took a few days last week as we had our 4 granddaughters for the week. The yearly get alone time with Nana and Papa, so it was the boat to the lake and the tube, fishing swimming, camp fires and cook outs.I did get a chance to change the PJ. I found a #15 PJ (stock is 17.5). Adjusting the fuel screw, unable to richen even @ 31/2 turns, and it would run with the F/S turned all the way in (where is that extra fuel?). Driving, throttle response was slow and you could tell that it was lean on the bottom end. WOT was OK.
I then changed the enrichner plunger (dia was same and needle end same, only diff. was body length, just what I had @ the time) increase spring preload pressure as well. No changeToday I removed carb and disassembled. Again inspected all parts and found no problems. I did check PJ with a set of wire gages and there was barely a difference between a 15 and 17.5, do not believe the 17.5 hole size as been damaged by anyone. I installed new o-ring/washer/spring on F/S - reinstalled stock enrichner plunger - adjusted enrichner cable free play to max. Put fresh fuel in the tank. I lowered the float height ( this carb has a angled bowl surface , not one that you can hold up and the float would be level with the surface)Reinstalled with no change - cold idle is fine and adjustable (F/S and idle speed) warm up and idle speed drops and eng will die. If you increase idle speed adjustment and then rev eng, idle will be high and then slow to normal and then slow and die. Adjusting the F/S at this time leaner makes no difference even @ closed, and no difference going richer.
When engine dies, restart is throttle open and just a few cranks of the eng. Let unit cool idle is fine again.
Note: the carb has not had any stale fuel in it ever, in fact very clean for the age.I did check spark as well with an adjustable gap, spark is not deep blue-wide band, but will not misfire out to 12mm. I did wire in a different coil (off a different unit) and it had a wider band and a deep blue color. Did not make a difference.
I had heard and experience flywheel problems, but mostly hard starting if start @ all, hit and miss spark etc. In some of my old spark plug diagnosis info for black / dry sooty plug - 1) rich/fuel 2) weak spark Well that didn't pan out !Any ideas, I am open.Yes I know Robert P, he left Yam and I had heard he was working for a car company in Cal. Joe P. and I did some testing and I did a lot with setting information for service. Joe moved to Cal. office for a few years with service and is now in Kennesaw Ga office. Did you know Mark Brozina western RSR? Mark and I did a lot of mountain sled testing together. Cudahy office moved to Pleasent Praire Wi around 2002-3. Just heard that new "North American Snowmobile Division" (Global Headquarters) is to be based in Toronto Ont. Canada, which means Pleasant Praire Snowmobile guy's are gone. In fact there are non of the guy's I worked with left, (few in Japan only) all new bunch of people. Time goes by fast and you kinda of lose track of thingsIf you wanted to call and talk it would be fun, my cell is(###) ###-#### home(###) ###-####Later TM
Expert:  RSRBOB replied 2 months ago.

I will give you a call over the week end. Talk to you then!


Customer: replied 2 months ago.
Sounds good
Looking forward to talking with you.
If we don't connect leave a number and I will get back to you.
Thanks TM
Customer: replied 2 months ago.
Morning Bob
Sorry we did not connect over the weekend. Was looking forward to a chat on the old days and what's up today.
Maybe tonightTom
Expert:  RSRBOB replied 2 months ago.

Hey, Saturday ended up being a lot busier for me than I anticipated. We will talk soon, Promise!

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