Update on Rough mid range problem

[jjsinaz]

Well, I bought a new used set of carbs for the GTX over the weekend for $60. Took them apart and they looked real clean inside, so I cleaned them with carb cleaner and blew everything out then reassembled them with the original parts. Only thing I had to replace was an o ring on one of the needle seats was leaking. Pop off was good about 37 psi on the MAG and 35 on the PTO. Adjusted the highs to 0 and lows to 1 turn out.

Took it out today and there was a noticeable improvement, although the 4 stroking in the midrange is still there, it is not nearly as bad and the idle is much smoother now. I think it still needs a bit of tweaking but I can tolerate the way it runs now.

I don't think I'll ever be able to get rid of the midrange problem all together anyway, and I really did not want to spend $400 on new carbs. Today was the most enjoyable day out so far this year!

 

[R-u-n2it]

You will eventually get rid of the mid range problem if you keep looking. Typically if there is a problem it keeps getting worse, not many logical reasons for something to start giving you a problem and then stop and stay there, and even less logical for it to go back to normal all on it's own, not impossible but highly unlikely. Try anything you can think of that you haven't already tried. Take springs out of RAVEs so they open right away just to see what happens when you are at normal opening RPMs to verify if it's only RAVES, partially RAVEs or nothing to do with RAVEs. If you DON"T look you might make your prediction come true.... Lee

 

[jjsinaz]

Thanks for the advice, and you're right, I'll never find it if I don't keep looking. I'm fairly convinced now that it's not the carbs. I'll try taking the RAVE springs out and see what happens. It does not have the slotted RAVE valves. I also need to check the housings to see if they are the old style. I was having a problem when I first got the ski with melting RAVE pistons and adjusters. I bought a used set of RAVEs from Westside and they sent me these. I don't understand why they would sell something that is known to have a TSB and cause problems. I probably should have asked them to exchange these for the updated version. The original RAVEs I had were the slotted type and the updated housings.

 

[esahlin]

jjsinaz-I know I have posted on the midrange threads before that it was my water regulator on my 96 GTX that caused my midrange problem. After rebuilding the water regulator the problem did subsided but......

However, I just rode the 96 GTX last week (my other family members have been the main riders since last year) and notice the same rough running flat spot at part throttle which basically lasts until the carbs get on the main circuit. Took the carbs off of the 96 GTX and put on 96 XP to see if I could mimic the problem.....same part throttle problem until 3/4 throttle till wide open.

Took the carbs off the xp and went through them and noticed that the carb throttle synchronization adjustable link was not adjusted well enough (the link that connects both carbs throttle levers). Meaning that the Mag carb throttle blade was sweeping past the three transition circuit holes in the carb body before the throttle blade on the PTO carb was. The MAG carb was swept past the third transition hole while the PTO carb throttle blade was between its 1st and second transition holes. Since it is the uncovering of these transition holes that determine the amount of fuel delivered during the transition circuit it looks to me like my PTO carb was way behind in its delivery during the part throttle transitions.

The adjustable synchronization link was only about three turns off so the synchronization seems easy to miss-adjust. To re-adjust the link easily and more accurately, I took an extra intake manifold (RV cover) that I had taken off another 787 and mounted the carbs to it off the ski. This to mimic on ski mounting and get accurate spacing between the carbs. Then I could more accurately see (by turning the intake manifold over to watch the throttle blades open) that my throttle blade sweeps of their transition holes were not synched up properly. Made a much more accurate way to set the synchronization rod.

I haven't tested the carbs yet on the water but I wanted to point this out as lots of us keep searching for causes of a midrange problem. This is something that doesn't cost $$$ just time and since everyone with this problem goes through their carbs often Its something easy to check.

I'll post up if my re-synchronization helps me out. I think I can already tell while running it on the trailer....but we all know trailer running is fantasy compared to in the water.

 

[jjsinaz]

That's a very interesting observation. I think you may be on to something here. I'll be curious to see how that works out for you. I did something similar to what you did with the intake manifold except I used the air box mount and bolted the carbs to it. I backed off the idle speed screw all the way and adjusted the throttle link so that when the mag throttle plate was completely closed the PTO was too. Don't know if that was a good method or not. I know with most engines that have multiple carbs, using a vacuum gauge is the more accurate method

And as far as running on the trailer, all you can say about that is "Yep, it runs".

 

[R-u-n2it]

When 1 carb is ahead of the other your RAVES are opening one before the other and that will make it rough running. The slotted ones will open and close easier. A backyard mechanic with patience could take a big flat file and use the edge to make the slots if you have more time than $ and the valves stems are good. You can sync your carbs on the engine, this is what I do, remove flame arrestors, back idle screw off stop, and hold an inspection mirror and real small led flashlight in 1 hand while working throttle linkage with the other and watch (looking for the least bit of movement) to see which one moves off carb throat 1st, adjust, when you can't tell which is moving 1st (the 1st is the one not touching carb throat wall) it's good. Lee

 

[jjsinaz]

I did basically the same thing you just described on the bench by bolting the carbs to the air box mount. Adjusted the linkage so that you could not tell one was moving ahead of the other. Sorry, but the inspection mirror thing ain't gonna work for me. When you get to be my age you have a hard enough time seeing something like that when it is right in front of you under a good light.

 

[mikidymac]

I use the sound. You can let them snap closed with your head over them and actually hear what one is making the noise, if you adjust too far the other one will make the snap and when you can’t tell a difference they are aligned. Been doing it this way for years.

 

[R-u-n2it]

I did basically the same thing you just described on the bench by bolting the carbs to the air box mount. Adjusted the linkage so that you could not tell one was moving ahead of the other. Sorry, but the inspection mirror thing ain't gonna work for me. When you get to be my age you have a hard enough time seeing something like that when it is right in front of you under a good light.

Heard that, I use one of those Harbor Freight things, like a hard hat head band with the eye part that swings up and down. And use a bright @$$ led light. How old are you, don't say you remember the Stanley Steamers.... I'm 66 and still going for it, if I could only remember what it is I'm going for {;o)

 

[R-u-n2it]

I use the sound. You can let them snap closed with your head over them and actually hear what one is making the noise, if you adjust too far the other one will make the snap and when you can’t tell a difference they are aligned. Been doing it this way for years.[/QUOTE

Just remembered I'm looking down 46MM Buckshots so a little more room to see, but the sound way doesn't take any extra tools, will have to try that. If you ran NOVIs you would have a couple red snappers....

 

[jjsinaz]

I'll have to try the sound method, although I'm sure that takes some time to learn. Sounds like you have a few years on me R-u. I turn 60 next month...and still going for it as well