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TIMOTO, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 1460
Experience:  Honda registered technician, silver level award, former Kawasaki/Suzuki tech, 40+ years exp.
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Hey Richard, I am scratching my head on a problem I have with

Customer Question

Hey Richard, I am scratching my head on a problem I have with my 1996 Honda Magna and at this point am completely out of ideas. The bike had a bunch of carb work (Jetting, needles & springs) done before I got it and I have brought it back to stock needles, stock springs and jets If I open it up full throttle the RPM's aren't rising as fast as they should and the bike sputters when it gets up around 8500 RPM's. I'f a let off the throttle a bit I seem to get a little more power, but the bike just cant seem to get past the 8500 mark in the upper gears.
Submitted: 2 years ago.
Category: Motorcycle
Expert:  TIMOTO replied 2 years ago.
I am assuming that the jet kit was a dynojet kit. The instillation of that kit involves drilling out the slide lift holes to change the lift rate of the slide in order to work with the springs and needles in the kit. If you want to go back to the stock components then you will need to buy new slides and that will be expensive. The best option is to reinstall the dynojet components along with the recommended main jets depending on wether you have stock exhaust or modified exhaust.
Customer: replied 2 years ago.
You are correct that it was a dynojet kit, but the slides were also replaced with a different set out of another set of carbs. The bike was running OK for a while after I did the change but seems to have developed this problem a few months back. The carbs are clean as a whistle inside and In the lower range of the throttle seem to be getting fairly good response.I ran the mix really thick to see if there was any changes and it actually seemed to get worse once it got into the upper RPM's. The problem also gets worse the faster you go. In the first two gears I get to 9500 without too much issue then it gets lower in 3rd and it can't get past 8500 in 4th and 5th. The slides move freely and there are no holes in the diaphragms. Vacuum petcock is good, fuel flows freely from the tank. The ignition system checked out within spec and the valves were checked last year. I also balanced the carbs checked to make sure there is no drag on the brakes, chain well lubed, no vacuum leaks I can find...Like I said it is a bit baffling.Unless both sets of slides had been drilled (the set I used was from a carb bank I bought) I don't think the bike would have ever run right. I can check the slides to be 100% sure though. Do you know what size the stock holes should be?
Expert:  TIMOTO replied 2 years ago.
No, I do not know the size of the oem holes. In the last two weeks I have done two of those but both bikes have since left. Dynojet has a website with a pdf file to download with install instructions which I believe shows the drill size that comes in the kit. I tried to download to my home computer but it will not open even though I do it all the time on the work computer. Another thing thing to check is the air filter for the atmospheric vent for the tops of the slide chambers. It is located under the left chrome over carbs inside the small black plastic housing. The foam element disintegrates and works its way into the carbs.
Customer: replied 2 years ago.
It was working fine for a while, but the performance has dropped off. The foam element is replaced every other season (Heard too many horror stories about the mess they make) as a part of PM. The Exhaust is aftermarket. They are baffled, but not much. Neither of these should be the culprit though as they were both on the bike when it was running strong.The drill bit is a #50 in the kit. I can take a ride up to harbor freight this weekend and pull the carbs again to see if there is something amiss there. The thing that concerns me here is that if the slides were drilled and that was what is causing the problem, I'd need to know what the OEM holes would need to be restored to. If I knew what the stock holes in the slides were I would just epoxy them shut and redrill it. Again though, I don't think this is an issue with the slides as it was running pretty good at one point, but I am more than willing to check it out to see where they are for sizing.I had 108's in there and dropped to 105's to see if it would help and it seemed like it did. This morning I richened to mix to see what it would do and the performance seemed pretty laggy. It also seemed to make the top end throttle response worse. Before I rode home I thinned the mix about 1/2 turn below where it was before I adjusted it up this morning and it was a bit more responsive on the way home tonight. while certainly not where I thought it should be it seemed less laggy on that last 1/4 of the throttle. I am considering dropping to a 102 to see if that makes it better or worse. I also have a 125, but that seems WAY too far in the opposite direction. I might put it in there just for giggles though...Any other suggestions?
Expert:  TIMOTO replied 2 years ago.
It sounds like the mixture is rich for some reason. I would try going sown one more size on the main jets to see improves or an alternative would be to remove the air filter. If it runs better then check the float bowl vent hose for restriction.
Customer: replied 2 years ago.
Yes it is very odd. I know the factory settings for the pilot screws are 2.5 turns and I am currently backed out to about 1.25. Obviously I don't want to run it too lean and the mains seem to be the place having the most difficulty I have a K&N Air filter I can install for testing purposes. That should let in a bit more air. If so I'll drop the mains down to the 102's and see if it improves any.
Expert:  TIMOTO replied 2 years ago.
Yes, try that next.