09-29-2012, 02:54 AM #1
proper indexing of oil pump on 95 SLT750
New to PWCs but not mechanics. Just assembled 2 SLTs from 3 broken skis. The first, a 94 was torn down cause it wouldn't rev up but the problem was actually fuel starvation from bad pickup lines inside the tank. Put the motor back together with parts from the 2nd SLT since it needed barrels, rings and a piston. Blew the inlet cooling hose off the pipe the first time out, swamped it and it overheated getting out of the lake. Blew 2 head gaskets, replaced them and it worked perfect afterward. 3rd ski is 95 parts only donor for the 2 94s. 2nd 94 had grenaded bottom end hence the 3rd boat with a good low hour motor and rough hull from running the upper Sacramento River. Swapped the 95 engine into the 94 using the 94 carbs/Vortex FAs and intake manifold, but added a set of V-Force reeds and SLX spacers. Problem I have is the 94s seem to use a vacume modulated(constant rate?) oil pump while the 95 has mechanical linkage to the carb(VRO?). With the spacers the carbs sit higher up than before and threw the oil pump out of adjustment. I didn't take note of the change till I already had the motor in the hull and figured I'd just try it first. Started up instantly before suffering a cdi failure. Put the 95 cdi in and presto it ran again. Problem is it smokes like mad, won't rev past 4k and verges on fouling the plugs. Jetting adjustments make zero difference because the oil/fuel ratio is so far out I can't find how the pump arm should be adjusted to deal with the repositioned carbs. My thought is the pump arm should be fully at the bottom of the stroke at closed throttle but I don't dare try that without some expert input. Any advice telling to dump the injection system will be appreciated but not heeded so probably save your fingertips the effort. I googled a bunch of info from here but can't find this one little detail. Great, helpful site, keep up the good work and thanx.
09-29-2012, 07:47 AM #2
Welcome to the Hulk!
The oil pumps which don't have linkage back to the carbs are not variable rate and therefore pump full oil volume all the time. In addition, the oil pumps which do have variable rates fail to the full oil volume position. I would think you should have the same performance / smoke characteristics between both oil pumps with the non variable rate pump smoking more than the other...... Otherwise, I would be looking for other issues, like a lack of fuel / lean condition causing more oil burn than fuel due to lack of fuel......?
09-29-2012, 02:08 PM #3
I've been a motorcycle mech 40 years. Fuel is not a problem, I changed out all lines, carbs are jetted up for flame arrestors, OP head and PSI pipe that were on the original motor. I reworked the fuel pump mounts and got the pulse line down to 4" and did the dual feed setup to the carbs. All 3 cylinders have good compression. Crank seals show no indication of leakage. It started instantly and settled into a perfect idle. After an hour of running all 3 plugs are black and wet. Glad I got out of the water before it quit. The old Mikuni oil pumps on Yammies, Kawis, Suzis had marks to set the pump to. I can't see any such mark on these pumps though. I found a thread here about adjusting the oil pump link on PTO carb throttle shaft and loosened up the nut but can't find anything to suggest setting marks on the pump or dimensions etc. Maybe I'll just set it to the minimun position and run premix till I figure it out. Oh yea, the restrictor IS in the return line.On the older oil pumps there's a nipple that I thought might be a caume fitting. It appears on closer examination that it's a bleed port. Can anybody confirm this? I might swap to the older pump for simplicity.
Last edited by valvesrule; 09-30-2012 at 06:04 PM.
10-01-2012, 01:36 PM #4
You may have to use the oil pump linkage from a 780 engine, these all had the reed spacers from the factory. The 94 oil pump isn't adjustable, the faster the engine runs, the more oil it pumps, the 95's pump about the same oil at wot, but uses less at low speed especially idle speed, therefore don't smoke as much. As bluefish says, if the linkage arm is removed from the carburetors, the pump defaults to full output all the time. That full output is more oil than would be pumped if the linkage was attached & you are at full throttle. Rather than screw something up by trying to make the 95 linkage work I would go to the 94 pump. I have a 94 SLT converted to 780 cylinders, reed spacers, 780 air filter etc, & use the 94 pump, it smokes less than when the engine was a 750 as the 780 used more fuel, but it still puts out enough oil for safe operation.
10-01-2012, 03:05 PM #5
From you last post, sounds like you are running the stock fuel pump and have implemented the dual feed with tees in between the carbs....? If that is the case, and if you haven't already done it, the trippple outlet fuel pump upgrade is very highly recommended for these skis.......
The pump should have one larger in nipple and three smaller out nipples. There is a bleed screw on the end facing the MAG cylinder....
10-02-2012, 02:04 AM #6
10-02-2012, 02:28 AM #7
10-02-2012, 07:03 AM #8
09-07-2014, 05:08 AM #9
2 years later and it still is an intermittent runner. I haven't been very diligent about solving this thing. V force reeds had sucked a petal in the mag cylinder and the rest didn't look so good either so stockers went back in. I keep getting recurring gas/jelly problems in the fuel even though it's been drained, flushed with carb cleaner/Berrymans and blown out with air pressure. Tank, sender, carbs, intake, fuel and oil pumps and CDI updated to the 95 stuff.
The oil pump problem is solved with by the variable pump and custom link, triple outlet pump installed. Hardly smokes at at idle, runs clean to 3500rpm then falls on it's face. Finally got it to accept idle mixture adjustments with best idle achieved at 1 to 1 1/4 turns giving a very good smooth idle. I tried every carb setting I could find for any 750/780 with poor results. Pretty sure it was the bad reeds.
So tomorrow I have to drag it 25 miles again to put it in the water and try to get the high speed screws to have effect.
Last edited by K447; 09-07-2014 at 08:09 AM.
09-07-2014, 08:19 AM #10
- Join Date
- Jul 2007
- near Toronto, Canada
I am also wondering if the fuel system is leaking air into the fuel hoses. The fuel pump creates suction in the fuel feed all the way from the fuel tank to the fuel pump itself. Oetiker type stepless/gapless ear clamps are my preference. They clamp evenly all the way around the hose and seal very well.
If the fuel selector valve is still original, replace it with new. There is a rubber seal piece inside that hardens with age and can allow air to enter the fuel feed.
The thinking here is that something is allowing air into the fuel system or is reacting with the fuel to cause gel to form.
If possible purchase non-ethanol gasoline and remove the ethanol blended old gasoline.
I did not read back to see whether you used genuine Mikuni carburetor rebuild kits with new needles and seats. Aftermarket carb kits can sometimes cause strange problems which cannot be tuned away.
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