Carb Tuning

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gap599

New member
Joined
Dec 3, 2012
Messages
56
Age
40
Location
Saskatoon, SK Canada
Hello everyone,

Last winter i burned down the motor in my SRX 700 (PTO cylinder was lean), and bought a used Mr Viper ported motor from a member here as a replacement. I finally got the new motor installed and have a few questions.

My carbs are set at:
Pilots 42.5
Mains 150
Needles 3rd clip position
fuel screws 2 turns out

1) How long do you have to run on new plugs to get a read on them? I ran the sled for about 10 min in the shop and then went for a qucik ride around the yard (about 1 mile). I pulled the plugs (see pics below) and they look very lean to me (especially the PTO side). I know i should be reading the plugs in conjunction with piston wash at different throttle positions, but i dont want to keep driving the sled if it is too lean.

2) it starts and idles great. mid range seems sluggish, top end seems okay (though i didnt try it much)

3) when i take off from idle, it runs okay (mid range seems sluggish), when i decelerate, then try to accelerate again it coughs and sputters and wont rev until i stop and let it idle for a few seconds, then i can take off okay.

I think i just need help getting the carbs dialed in, any help is greatly apreciated!

Thanks

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Yes my SRX did something similar and I burned a piston. Don't drive it until you find the problem because it's certainly a lack of fuel so it's running lean and without lubrication. I would check fuel filter, fuel leaks, clean carbs, carb boots. Good luck
 
Yeah, thanks Sledneck. When I swapped motors I changed the fuel filter and cleaned the carbs, so i dont think either of those are the problem.
 
Plugs don't look horrible to me, (better pic might help) they look rather new though. Reading a new plug is very hard, do you have some used ones laying around? Whats the was look like? (top of piston) Porting sometimes make wash hard to read as well. As far as the acting up when getting back onto the gas that sounds like a TORS issue to me.
 
Thanks Devillin AblueDress. I'll double check the throttle cable in case it is a tors issue. You're right, the plugs are new - only ran them for a mile. I don't have any old ones to compare to as this is the first time I ran this motor. The plugs. From my old motor were always much darker.
 
gap599 said:
The plugs. From my old motor were always much darker.
Click to expand...

A good portion of the "much darker" is mostly due to it being an older plug. It being a new plug your "burn" doesn't show up very well. With an already dark plug its easy to tell if its getting darker/lighter or staying the same. Did this motor come from Blackedout96? What was PO running for jetting? Maybe a jetting suggestion from Mr.Viper as he did the porting.
 
Yeah, it is the motor from Blackedout96. I did get jetting recomendations from Mr Viper, which is what i used, except i have the fuel screws at 2 turns instead of 1.5, becasue I wanted to start on the rich side. How long does it take for the plugs to change colour?

The other thing thats bugging me is the PTO side looks leaner, and that is the cylinder that burned down previously. Any idea why the one cylinder is leaner? Its a different motor, so that should rule out crank seals, and carb boots. The carbs were also just thoughly cleaned, so shouldnt be a dirty carb. What else could it be?
 
Have you contacted Mrviper and asked him what to jet it to? Nobody is going to know what to jet it to better than the man who built it. I bought one of his motors used and even though he didn't make a penny off me from that motor he still had no problem telling me where to jet and clutch it.

Edit, just noticed your last post....still hes the guy you want to ask.
 
As far as plugs coloring that will depend on how you ride it, gas used and type of oil used. I am assuming you used some sort of aerosol to check for air leaks? Same carbs from previous burn down cylinder? Did you find the root cause on that one?
 
Also, other than being able to tell the two on the right are darker than the other one the pics are about useless. When you blow them up they are just a blur. maybe try to get a better pic.
 
so the pto cylinder blew up in your last engine and now this engine the pto is also leaner???.................... that tells me you need to look into your carbs and pay paticular attention to the pto one as theres something going on there then.

I see your in Canada, so you only are going to be running 91 octane in that sled as well right? Since your going to have the carbs off to check the pto cylinder, i would bump your needles up to 3.25 in it, the mains will be fine at 150 UNLESS you have a gutted airbox or cold air kit. If you have those things youll need to jet it up more.

If you ride alot at near the 10degrees down to zero degrees faren. youll need 152.5 mains

2 turns out on the fuel screws wont hurt anything.

what do you have in the sled for clutching and gears?

if its coughs and sputters and then goes fine after you stop and idle, the throttle cable is too tight and triggering the tors switch, loosen up the adjuster.
 
Thanks for your help and suggestions everyone. It is really helpful.

I will try to get a better pic of the plugs tomorrow AM.

I did not find the root cause of the previous melt down. I was hopeful that by swapping motors and going through the carbs the problem wouldnt follow. Guess I may be wrong!

Mr Viper, It gets real cold here, A lot of my riding would be at 0f to -10f, so I'll pick up a set of 152.5mains (or should I go even bigger?) and move the needles to 3.25. The airbox is stock. Only mod is hauck growlers.

I went through the carbs thoughly and didnt find anything out of the ordinary with the PTO one (I am by no means an expert though). I installed new pilots and mains in all three. I'll go through the carbs again when I'm swapping jets/adjusting needles. Any tips/suggestions what to look for?

I double checked the throttle cable and adjusted it, it was a little tight. Hopefully that takes care of that issue but i dont want to run the sled to check until I get the PTO carb issue solved.

I filled the fuel tank with premix (50:1) just in case there was any air in the oil pump. This shouldn't affect the A/F ratio drastically should it?
 
Also,

Primary Clutch - red spring

Secondary Clutch - Bender helix, black spring with green stripe in 6 position (let me know if im missing anything - clutching is pretty new to me)

Gears are stock.
 
well the 50:1 oil and gas plus the oil pump running at 50;1 makes for a leaner air fuel ratio because theres more oil then gas so it makes it leaner not richer, you dont need to do that, drain a bit out and fill with just gas, dump the other in your weedwhip and chainsaws,leafblowers. its not major problem but its adding to it.

for the clutch youll need to explain a bit better then that, like the weights will have letters on them if yamaha and the helix will have markings if aftermarket.
if your unsure, post pics ansd someone can identify what you have, but the lets focus first on the engine running lean.

152.5 mains will be fine in it. The needles set to 3.25 is the 4th groove down on the needle from the short end with BOTH of the plasitc shims on top of the clip. Youll need a ballend 2.5mm allen wrench to do those. 42.5 pilots are fine, fuel screws can likely put at 1.75 turns out from lightly seated.

I would pull the bowl off that pto carb, remove the pilot jet and squirt carb cleaner up into the orfice in the carb where the pilot jet screws in, the fuel should come out of the front of the carb in the floor of the throat in front of the slide.

then i would remove the float pin and pull the needle and seat, theres a small phillips head screw to remove then you can pulll the seat from the carb, check the little screen on the seat, see if its gooped up. When you put it back together check to see the float arm sits level with the top carb body surface where the bowl bolts on, you flip the carb upside down and it shopuld be the same plane.
 
put 47.5 pilots in it and 156.3 mains and run it do a plug check if your just riding it around the yard your just running on pilot jets so thats fine do a plug check but then you have to open it up and hit kill switch and do plug check but 150 is to little I have srx thats ported and I am running 47.5 and 156.3 that will be a good place to start
 
Hey guys, i'm back at work now (I work away from home). I was hoping to get this project sorted out before I left, but just didnt have the time. I should be back home in 10 days or so, I'll continue working on it then. Mr Viper, I'll get some bigger mains, and go through the carbs completely again and get back to you with my findings/results. I get some more info regarding my clutching too. Thanks again for all your help everyone!
 
Well i'm finally home from a long shift at work. Yesterday I pulled the carbs and cleaned them again - i didnt find anything out of the ordinary. I also decided to replace the three fuel lines between the pump and carbs, and the PTO carb fuel line was cracked (strange that i didnt notice leaking fuel). I put everything back together and went for a quick test ride, all 3 plugs are a similar colour now so hopefully that was the problem that was causing the lean condition.

I also switched to 152.5 mains, moved the needles to 3.25 and set the fuel screws at 1.75 turns out as per Mr. Vipers recomendations (kept the pilots at 42.5). I only went for a quick test ride (2 mi), it seemed to be running good but did have an idle hang - after letting off the gas, would idle aroung 3,000 until i gave the choke i quick pull, then would settle down to 1,800. I did a search on this and it seems the idle hang is caused by a lean condition at idle. What are your recomendations to get ride of it? further out with the fuel screws? bigger pilots?
 
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