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AimlessMoto

1995 Suzuki Quadrunner 250, Idles, bogs 1/4 throttle, fine on top end.

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Hey guys, new here, but haven't found ANY answer to my specific problem on a Suzuki dedicated ATV forum, so here's to hoping!

I acquired a 95' Quadrunner 250, 4x4, (LT4WD) for practically nothing with no spark. The PO had tossed in a used stator which didn't fix the problem... so I went all routes (though cheaply) to narrow down the initial problem of no spark. 

Plug, coil, CDI (caltric) and stator w/pickup (caltric) were purchased and installed. And it RAN, but bogged horribly and would not rev past 1/4 throttle. 

I checked fuel flow, vacuum lines, all the normal stuff, no issues. I decided to check the valves and cam... well, there was one problem. The cam was 1mm under the lowest spec in the manual. So, in-came a new cam, Stage 1 Hotcams... also threw in a new set of shindy valves, lapped them, replaced the valve seals, and the timing chain. 

Back together again (w/stock airbox and new oiled filter). Now it idles even better, still boggs at 1/4 throttle, but will rev past it if you hold the throttle open for a second. Ahaha... success!

So I was able to ride it above 1/4 throttle once I had momentum... could shift through the gears, all was good as long as I kept it over 1/2 throttle. Took a long enough ride to break in the cam properly at least so I won't have to worry about that. 

Now, I start fiddling with the carb. It's clean as a whistle, stock, with stock jets (new replacement Mikuni jets). Same problem. 

 

I start thinking, maybe this is fuel related and the bike is having an issue transitioning from idle jet to main jet... so I LOWER the needle by raising the clip 1 spot. Now it revvs up in neutral with no bog, but it boggs about the same trying to ride it. So I move the needle down again with the clip on the top slot. Better, but still has a bit of bog at 1/4 throttle. 

The last bit of advice I got was to ditch the CV carb... so I sprung for a brand new Mikuni VM30-83 round-slide. Bolted it up, blew into the vacuum tube to fill it with fuel (no vacuum port on this one) and she fired right up... but there is still a bit of bog, it's just masked by the fact that I'm not waiting for the vacuum diaphragm to open. 

 

So I feel like each little step brings me closer, but not perfect. I'm now wondering if this is still in-fact a carb tuning issue (I have some jets I can fiddle with and maybe lean-out the idle jet a little.) OR if the cheap-a** Caltric Stator/Pickup is what's causing these issues. 

 

I have a 95' KingQuad with 400 miles on it... like new.. runs like a top... I've tried both the stock QR and the Caltric CDI boxes on it, and it revvs up and runs like a champ. 

 

The only unknowns between the two systems are the carb, and the stator/pickup. My next step in troubleshooting is to rip apart the King Quad and test it's CDI on the Quadrunner... but considering there is no change to how it runs I doubt it will lead to a solution. 

 

HOWEVER... I tried the stock CDI just recently after running the Caltric this whole time, and the bike runs like garbage. Hardly idles, and won't rev up at all. So, that is my one smoking gun telling me that it's either the pickup coil or the stator itself. 

 

Has anyone had a problem even CLOSE to this? I can't image the carb would be causing this many issues, especially going to 2 different ones, both with stock jetting to OEM, and exhibiting the identical symptoms... the only change is when different CDI's are plugged in, or when the needle valve leans out the mixture. 

Also, I checked the piston, rings and bore when I had it apart and they're like-new... no scoring, rings are loose, cylinder is still round and has honing marks still int he bore. Stock piston, stock bore size and it has 160psi compression. Battery is brand new, and I've tried 3 different R/R's, none of which change any symptoms, but slightly vary the charging voltage by .2-.5 of a volt depending on which unit. Also tried a new coil which changed nothing. 

ANY help would be appreciated. Too much invested to not get it running right. 

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Here's a video of it as received and up-to actually riding it. You be the judge! (there is a lot of banter, feel free to skip around). Ride portion is the last 4 mins of the video, 12:22 is how it was before the head rebuild... fluttering and stuttering at 1/4 throttle. 

 

Edited by AimlessMoto
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Have you checked the rectifier and voltage coming to the battery ?  I’m curious to see what you have as far as voltage. Rev the engine a bit and see what’s happening.  

 

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I just tried all 3. The results are:

Battery was a steady 13.00v prior to test. 

Electrosport: 14.0v idle, 14.4v rev.

Caltric: 13.8v idle, 13.9v rev.

Suzuki (original): 13.9v idle, 13.6v rev. 

The ride and running videos were all with the Electrosport unit installed. 

15611336909781638369830.jpg

Edited by AimlessMoto

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I just did a no-load test on the AC stator. Set the meter to AC 200V... only getting about 50v per each leg when held at high revs. Me-thinks it may be the issue... which sucks. 3x opening the damn engine, the last time to install this new Caltric stator. So upset. 

 

1561135297753657053136.jpg

Edited by AimlessMoto

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Well it’s a last ditch effort.  You should test the stator on ohms setting phase to phase and see if the numbers are within range.  

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32 minutes ago, Frank Angerano said:

Well it’s a last ditch effort.  You should test the stator on ohms setting phase to phase and see if the numbers are within range.  

While running?

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Engine off and tester on ohms, phase to phase you should get a reading. Somewhere in the 100’s maybe, It’s in the manual. Test each wire to wire and see what you get.  

Do this with the pick up coil also.  

I like to test both ways.  One when the bike is ice cold.   Second is when the engine is hot.  

Most of the time stators go bad and you don’t  have the option of testing while hot because you have no spark.   

The acceptable range will be listed in the manual.  

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39 minutes ago, Frank Angerano said:

Engine off and tester on ohms, phase to phase you should get a reading. Somewhere in the 100’s maybe, It’s in the manual. Test each wire to wire and see what you get.  

Do this with the pick up coil also.  

I like to test both ways.  One when the bike is ice cold.   Second is when the engine is hot.  

Most of the time stators go bad and you don’t  have the option of testing while hot because you have no spark.   

The acceptable range will be listed in the manual.  

Sounds good! I did the same test on my r/r and CDI... basic diode resistance test. I'll try that out when I get a minute this weekend and report back! Thanks for the help!

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I have had similar problems on a couple of machines, one solution was replacing a faulty aftermarket cdi box, another problem for a different machine was a vacuum leak at boot between carb and cylinder head

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On 6/23/2019 at 6:43 PM, Cj Winds said:

I have had similar problems on a couple of machines, one solution was replacing a faulty aftermarket cdi box, another problem for a different machine was a vacuum leak at boot between carb and cylinder head

I have run 2 different CDI's, and the problem is worse with the stock one... but with a spark tester I have no deviation in spark... it seems to be the mixture. Then again, still unsure if the mixture is just masking the problem. It does run REALLY well once it gets over the hump. 

 

I did complain to Caltric about the low voltage coming out of the stator and they send me a brand new one at no cost. I am tempted to sell it online and put the money towards getting my stock one rebuilt by Ricks Electronics. 

 

I have tossed at VM30 Mikuni on the bike for right now and it SEEMS to be a lot better... (was going to upgrade anyway). I may bite the bullet on another CDI, possibly a used eBay one rather than another Chinese POS. 

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I’ve never had any luck with aftermarket cheap cdi units.  Always like the oem cdi when it comes down to it.

The Chinese ones look great plug right in but are worthless.  Ive been lucky with caltrec stator coils though.  So far used a few and they’ve been good. 

Thats a great carburetor you put on. Prob cost a bit! $$$ but well worth it.  

 

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Cool video.

 

Does your idle jet have a spring, o-ring and seating washer? ie, all the parts are there?

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59 minutes ago, Ed Zeppeli said:

 

Cool video.

 

Does your idle jet have a spring, o-ring and seating washer? ie, all the parts are there?

 

1 hour ago, Frank Angerano said:

I’ve never had any luck with aftermarket cheap cdi units.  Always like the oem cdi when it comes down to it.

The Chinese ones look great plug right in but are worthless.  Ive been lucky with caltrec stator coils though.  So far used a few and they’ve been good. 

Thats a great carburetor you put on. Prob cost a bit! $$$ but well worth it.  

 

$70 on Amazon! Genuine mikuni, almost a direct copy of the one on the 87-89 Quadrunner! 

59 minutes ago, Ed Zeppeli said:

 

Cool video.

 

Does your idle jet have a spring, o-ring and seating washer? ie, all the parts are there?

Yup! All new on the CV in the video. Jet was 2.5 turns out. Tried 3, tried 2... both only affected the over-all idle and not the bogg issue. 

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When you describe the issue as being at 1/4 throttle only it kind of rules out spark in my mind and I keep going back to thinking something's up with the carb transitioning from idle circuit to main jet.

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the 3 most common things i have seen cause erratic running on these is 1) a plugged fuel tank vent (either improper routing or our friendly mud dauber hornets). 2) is a tiny hole in the fuel pump diaphram (at idle there isn't enough fuel draw, and at WOT there is so much of a pulse it can overcome the leak), and 3) is a delaminating intake manifold. they can delaminate internally as well as externally, so its not always easy to see. the test for the manifold leak is to have the machine idling (engine just warm enough to run without choke), and spray the manifold with water while grabbing the carb moving it in every direction. / its really difficult when you have 2 systems that can be at fault (in this case both electrical and fuel).  the fuel system is easier to diagnose than the electrical, so go there first. i will add that most (but definitely not all) of the electrical problems i saw in the 40 years of doing this was related to a bad ground. a quick way to eliminate that is to run a single wire from a GOOD CLEAN (meaning sanding, filing,etc. all of the paint off) chassis ground, to a CLEAN bolt on the engine case, to the battery - terminal, and then make certain the voltage regulator and CDI box and ignition coil all have CLEAN & TIGHT contacts as well. oh, something else just popped into my head, i have seen a few cases where the ignition coil connector was worked oversize from vibration causing intermittent ignition at specific rpms. tightening the contacts up by either replacing or bending them to increase the tension fixes that. its a lot of things, but i hope it helps.

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