Hi,
We have an old 1998 senior engine I have been using just to get a feel for 177 non MSA. We have done a lot of mini and junior MSA racing in the past with my lad, but we don't have much experience on senior.
My issue is we can't get the engine to rev - possibly max 13000 is all we can see. Many run to 14000 - 14300 (maybe with black coil). People at the track say it sounds different to other seniors??
Just looking for a few ideas on what it might be running through this below;
(1) Gearing, we geared it very low circa 4 teeth more than those revving to 14K to get revs - it seems to get to top revs at about 13000 and then stay there with no more to come.
(2) Battery, we messed about with some old batteries that struggled to turn over the starter and with the bendix whirring out, so bit the bullet and got a new lightweight lithium battery. Seems to start OK and run OK, haven't checked the actual voltage when fully charged on the optimate, perhaps I should check with the engine running??
(3) Loom, it has the original loom, could it be that, an expensive test to buy new to find it's not that!! Maybe run another complete engine set up to test the loom only - if it revs OK it's not the loom??
(4) Exhaust, It has the original 1998 exhaust with the original wadding as the rivets have only just been drilled out! We ran with this to start with, then put new wadding in with the wire wool mesh and as part of this process when we pulled the baffle our it was broken through half way along it's length rather than broken up at the end where it usually goes, so we put a new baffle in as well. When we found this we thought hey presto - that's it - especially with the comments from many at the track it sounds different. But no real change in revs.
(5) Coil / lead / cap, It has a black coil - original !1998 we suspect. The plug cap was a little ropey inside leaving rubber 'dust' on the plug after a run, so we replaced that with new along with the lead. No difference on revs. We then borrowed a green coil from a very kind gent - friend of ours - his top race coil. The engine felt a little smoother and possibly stronger but revs still down.
(6) Driver, Meaning the driver is sh*t; not driving fast enough to pull the revs - the driver is me on my second only outing so possibly yes! But my lad is fast and he went out on two sessions and was much faster than I but still couldn't pull the revs.
(7) Reed block, Dunno how this could affect revs, but I had what I think is a good spare reed block and the engine isn't sealed through the reed block - sealed a while ago. So swapped the reed block - the old one looked OK. The engine ran OK but still didn't rev.
(8) Air box, old style air box, has been apart, looks OK, I have a spare which I could try. Can't imagine it's that.
(9) Jetting, It was cold and reasonably high pressure and I'm learning to drive, so I ran a larger main jet than what others were running - 168 to start with then 165. With both it didn't rev beyond 13K. Big jet should give top end and / or loose any suggestion of missing at top end. On driving it didn't seem to give top end popping or missing - just maxed out on the revs it wanted to go and didn't pull further revs.
(10) Carb, It has the original 1998 carb, so it should be good. I have done a complete strip down, ultrasonic clean and rebuild. Down to venture out, all loose components out, cleaned, re installed. The engine runs OK but doesn't pull the revs. I could try a carb from an engine that is revving to 'eliminate that from our enquiries'!!
(11) Engine, The engine had been stood for a long while and we believe it has done relatively low hours, exhaust still had rivets in, piston coating (low carbon or no carbon on piston crown - side skirt looks low wear) looks like low hours. Could it be related to that. Engine was last sealed in 2004 and we believe has had had very little use since then. The crank has no noticeable end float, so it either / or hasn't done many hours and / or hasn't been fiched to generate end float and a more free running crank to produce revs. I can't imagine this would restrict revs to the tune of 1000 plus though? I might be wrong. When the engine was first tried after a long layup the crank seals went pressurising the transfer gear case and blowing out the oil. New crank seals were fitted and there is no trace of oil blowing out - catch tank has nothing in it. Does the engine just need a rebuild - bottom end / top end and why??
(12) fuel pump, we are running without a fuel line filter (filter in carb and filter the fuel going into the tank). The pump was from a batch I had, which is untested, not sure how to determine if it needs re kitting or not. I have other pumps which are also an unknown, I could track test those, or just re kit one pump so I know it's good. How can a sub standard pump affect revs - fuel starvation? How would that show on the track - leaning off at top end???? Popping etc, as noted above this was not evident - just not pulling the revs.
Any ideas how I can test to find the issue - just try swapping components we know are OK, beg / borrow etc. Don't want to spend too much on this set up as just running for the next few months to see if I can pick up the driving lark and if it's for me and if so we will invest more in a newer engine / chassis etc.
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Rotax senior revs by 'TeamPoor' << You are here!
