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After changed jetting bike is so hard to start

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Did some jetting changes and jetted myself into a corner :bonk: When the bike is super hard to start and stalls sometimes, what jetting condition is this? To rich or lean? I don't know which way is up right now, so its hard to tune my way outta this one :smirk:

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Pilot jet and or fuel screw.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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Figured you'd say that ;p what if my idle is super outta wack, how many turns out ballpark should it be? I had the bike stated then it kinda started to fade so I was trying to tweak the idle. Forgot which way was up and now the bike wont start. The idle is so far off I can't even do the pilot screw procedure. .... is there a idle procedure?!

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Figured you'd say that ;p what if my idle is super outta wack, how many turns out ballpark should it be? I had the bike stated then it kinda started to fade so I was trying to tweak the idle. Forgot which way was up and now the bike wont start. The idle is so far off I can't even do the pilot screw procedure. .... is there a idle procedure?!

Just turn the screw in a bunch, set your fuel screw to 1.5, and get it running. Adjust fuel screw for max idle.

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Tun the idle speed knob until the throttle slide is about 3/32nd's open. Fire the bike up. If it races, turn it down in 1/8 of a turn increments.Clockwise turns of the idle speed knob speeds the idle up.

When setting the fuel screw and proper idle speed, sometimes only a 1/16 of a turn is all that is needed. Tweak, ride 30 feet, stop, let it setle, tweak. Some bike can be tempermental.

Finally, you should never go wild and just change things 'because'. Only change the circuit that affects a problem. Never, ever make a change because some magazine/guy/whomever said to do this or that change.

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Goon! You are all over this site about your jetting. One day it's good, the next day it's bad, one day it's lean, the next it's rich. I posted up on the R&D Power Bowl a few weeks ago and you asked a few questions about it and that was it. That Power Bowl is by far the best thing you can put on your carb for tuning. It just simply works and works great. I could see the hesitation on purchasing one at $249 but I posted the site where you can get one for $150, free shipping and no tax. Your time has to be worth something and your jetting still is not correct as you say. Pry open your wallet and just purchase one and get back to having fun riding.

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Haha, yea yea i know. Well I've been adding mods to my new bike in stages, so It always seems to need jetting changes along w/ them according to the JD kit.. This bike seems to be real tempermental to any changes. And I've been trying to get rid of the imfamous bog, which I finally did, the bike was running crazy awesome but had this little rich gargle, so instead of trying to tweak it out w/ the fuel screw, I put my stupid cap on and decided to move the clip up 1 to lean it out. Bike was awesome at 3/4 turns out, so I thought my pilot was to large then. I wanted to have some room to play w/ it since I live at the foothills of the N. Ga mountains. Went down in the pilot, decided to drop the clip to compensaite and in the process went ahead and put the 165 main in I had. Bad move. All I did was jet it to JD spec and thats when my jetting spiraled outta control. Its my idle and pilot, I'm just having trouble dialing them in together. It's been a headache, but I've learned alot about my bike. I hate having to take it to the shop everytime I need a jet changed or something. I need to be able to do alot of this stuff myself. Thanks for the help again guys.

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When I was finally getting the bike started it was running super rough and real smokey. This bike has never ran like that and I couldn't understand why the same jetting that worked so well would now make the bike run super rough and not stay running unless I was twisting the throttle. I finally checked the plug, even though it is a month old and one of those $17 NGK's. Black as hell. Also I checked my oil 1st and it seemed low and super black on the kick starter side.. Not sure what caused it to be low and so black. I change my oil every 100 miles and it always looks brand new when I change it. This time I let it go to almost 200 for whatever reason. Anyways, then I checked the plug and its fouled like hell. It didn't even cross my mind because of the 3 thumpers I've had in the past year, I put a new plug in each of them around the time of purchase and never looked back. Do you guys know how & why a 4s fouls a plug so bad? I'm still learning w/ these bikes as I've only been riding and working on them for a year now. I hope after I put a new plug in it tommrow it w/ fire right up . :smirk:

Edited by GoonSquadRMZ450

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Do you leve the petcock on? Fuel can dribble into the engine, esp. when transporting and it can dilute the oil. Oil diluted fuel can make an engine run overly rich.

I know you've made a lot of jetting changes and from what I have read, not in the proper, logical order. You are supposed to:

set the float height

select the correct pilot-idle

Selct the main-WOT 4th/5th gear

Select the needle (straight diameter)-just off idle, below 1/4 throttle, under load

Clip position-over 1/2 throttle

Change the needle if the clip is not in the middle of the adjustment range

Recheck the main selection

Setup the AP-the 'Bog', leanest (largest) leak jet, with the timing correct

Each of these should be done one at a time with proper testing.

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I understand. I've only changed 3 jets. Pilot, main and needle. I've used 3 different sizes of the M&P, and only 2 clip positions on the needle. At 1st I started w/ the main, pilot and then the needle/clip. Def not in the order of your list. I was thinking I may need to take the carb off, clean it and the jets since I dont know if its ever been cleaned. Could it be a possibility that there is some trash in the carb/jets since I've opened it up and changed jets out a few times? Could that keep it from starting if something got into the pilot or air jets? I guess it wouldn't hurt to take it apart and clean it this weekend since its gonna be raining and then when I'm done, I will have a clean slate to start this testing procedure with. The float bowl height is something I'm not familiar with and I haven't done anything with the leak jet. What would you recommend for these 2 things?

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I took the carb off today while I was going back checking what I had done the other day (changed pilot, main and needle position) and when I put the pilot and main in, I just twist the carb and do it from the bottom. Pain in the ass. Well I thought I had the pilot all the way in, but it wasn't. What a dumb-ass rookie mistake! It was in the bottom of the bowl. So I hope that was the problem. It was hanging on when the bike 1st started and it ran great. Then after idling for a min when I thought I had adjusted the idle wrong, it just vibrated out and wouldn't start after that. I'll finish putting it back together in the am.. While I had it torn apart I was looking at the l linkage, I think, and it was spraying against the wall of the carb. Where should it be spraying excatly and how do I adjust it?

Edited by GoonSquadRMZ450

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I took it apart yesterday and cleaned it up and made sure everything was in there good and seated. I've done it the other way (through the hole) 4-5x and it was always really hard and I'd get someone to hold the carb, but I just made a mistake this time. Riding is nothing new to me, but 4 stroke carbs are. Only had them for about a year now. But thank you for you help and patience. I rode all day today and I'm still running rich on the needle. It had that gargle @ 1/4 throttle again and could not work it out w/ the fuel screw (@ max idle) Its working flawlessly w/ the pilot and main. Super crisp and snappy, fires right up, purrs on the idle. What can I do besides try leaner positions on the needle if the pilot, fuel screw and main are where they need to be? Thanks...

Edited by GoonSquadRMZ450

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Fuel screw is for idle ONLY!!!! Set it for a perfect idle and leave it ALONE.

Poor running below 1/4 throttle is the needle straight diameter. You need to try a different (possibly leaner) needle - Last letter needs to be a step higher in the alphabet.

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