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Post by Bronson7 on Feb 9, 2005 13:23:17 GMT -5
Well, on my SR500, I have a #25 pilot jet and a few mainjets of different sizes comming. The problem I'm currently having is my SR won't go above 70 mph. There's more throttle left but it just won't respond. I purchased the bike with a SuperTrapp exhaust and I don't think it was jetted for it. This fall, when the temps were about 80F, I was getting severe spark knock (pinging) at full throttle. I'm surmising that I'm just not getting enough gas in the upper range (main jet?). When I pulled the plug to read it, it had a nice brown color but that may be from mid range operation. Also I'm using a lead substitute which seams to leave a brown powdery residue on the plugs which may mask the true color. My plan is to go to the larger pilot and mainjet and see how that works out. In the interim, I'll stop using the lead additive in order to get a more true color. If this works out, the Minton mod will be next. Any suggestions? Does this sound like the correct approach/diagnosis?
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Post by motomick on Feb 11, 2005 9:18:09 GMT -5
fuel additive theory sounds ok,i would leave the pilot alone till you sort topend out?(1 change at a time),you don't say what size mains your'e running,has the fuel a high enough octane rating?,you might have to back the advance off a tad to stop the pinging?,hth,cheers Mick  |
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Post by Bronson7 on Feb 11, 2005 11:39:24 GMT -5
Yeah Mick, I agree. One step at a time. I'll do the main jet first. I should be getting them anyday day now. There's no provision for adjusting the timming unless I remove the stator and elongate the mount holes in order to be able to rotate it some. I checked the timming with a strobe and it is running a little advanced but then the marks on my flywheel look nothing like the ones I've been seeing in the manuals. Even Yamaha says that there is some adjustment, but not on mine. Maybe the '81's were a bit different. I'm hoping that perhaps a too lean condition is causing the ping. I'm using 93 Octane unleaded. Minimum, according to my manual is 91. I've added the lead substitute because these were intended to be run on leaded fuel, but here in the States, it's no longer available. The bike runs great till I get at about 3/4 throttle and it just peters out at about 70. I'll not use the lead substitute again till I get an accurate plug reading. Thanks Mick. I'll welcome any ideas and keep you posted.  Bronson7 |
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Post by Bronson7 on Feb 11, 2005 11:48:09 GMT -5
Oh, I forgot Mick. I believe it's running the stock main jet of 260, however I don't know for sure till I open it up . the carb is VM32SS. I have on order several sizes going up to 300. Thanks.
Bronson7
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Post by chairman on Feb 14, 2005 7:24:05 GMT -5
There's no provision for adjusting the timming unless I remove the stator and elongate the mount holes in order to be able to rotate it some. I checked the timming with a strobe and it is running a little advanced but then the marks on my flywheel look nothing like the ones I've been seeing in the manuals. Bronson7 Let me guess - timing marks are at 10, 20, 30 & 40 degrees? "F" is a band about 5degrees wide rather than a single mark? This is the setup on my SR and I also have a backing plate with no adjustment. Last weekend I elongated the holes and retarded the ignition a few degrees but it is still advanced. I did the trigonometry and the region marked "F" is nowhere near 7degrees BTDC. I don't have any more adjustment because the Hall Effect sensor is almost hard up against the inside of the flywheel case. Anyone who can tell me more about my set-up will have my gratitude. |
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Post by Bronson7 on Feb 14, 2005 11:02:57 GMT -5
You got it Chairman. That's exactly my set-up. Doesn't make much sense. I've decided to leave the timming alone for the time being and just concentrate on getting the jetting down. I went on a nice scenic 100 mile jaunt day before yesterday and almost got her up to 80. I'm figuring this bike must have sat for along time to only have 11,500 miles when I bought it, so partially clogged jets are a possibility and they may be slowly cleaning themselves up. Anyway, I'm eagerly awaiting my jets. If you should find more info on our timing set-up, please let me know and until then, happy riding.
Bronson7
ps Another glorious winter day and I'm off on my SR!
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Post by batmanron on Feb 26, 2005 6:51:03 GMT -5
Hi Bronson, got that bike running right yet? What does your bike rev to? I have a few SR's and and have come across the problem of "Choking up" on the throttle at about 4000 twice when I have purchased them and recently on my caferacer after installing another carby. This has been caused by various things I will list them The Muffler is not free flowing enough. The SR500 likes a free flowing pipe, but not completey straight through. If I think the muffler is the problem I take it for a quick lap with just the pipe attached -love that sound;D The Carburettor is running too rich or the float level is too high or has vibrated up. I service my regularly run SR carby every 3 months the float level seems to vibrate up a touch over that time. One further thing is that there is a vacuum diagphram on the very base of the carby. Its under a triangle part, this can become perferated after a while sitting and fuel can be sucked into the engine this is what my most recent discovery is. On all these times the plug does look black though, let us know how you go. Good Luck Thumping Downunder Batmanron  |
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Post by chairman on Feb 27, 2005 22:00:52 GMT -5
Oh, I forgot Mick. I believe it's running the stock main jet of 260, however I don't know for sure till I open it up . the carb is VM32SS. I have on order several sizes going up to 300. Thanks. Bronson7 G'day again, Bronson7 I also had a flat spot just past 1/2 throttle (about 125km/h in top gear) and the bike wouldn't accelerate beyond that. I raised the needle to the 4th clip setting, and upped the main jet to #330 (I have the 34mm carb, so this is an increase of 3 sizes) This has made a big difference, but I'm going up another size on the main jet looking for a bit more as it now runs out about 135km/h I have a slip-on air filter (K&H) and an almost straight-through exhaust. I've done some of the the Vonderhey mods - machined 0.05thou of the bottom of the slide and now made the needle setting and main jets a bit richer. I haven't drilled the needle jet but I got the impression that this would deliver a marginal improvement so it will be a last resort (the needle jet is expensive to replace if I stuff it up). |
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Post by Bronson7 on Mar 29, 2005 12:13:20 GMT -5
Hey Chairman, sorry I havn't got back with you all, but I ran into some personal problems that kept me occupied. Anyway, all is well and life is good. I have'nt done anything since I last posted but when I get back from Florida it's going to be hot and heavy on the SR. Been riding it quite a bit lately and going out today on a 120 mile run. I still plan on changing jets and installing a K&N filter to the stock box along with the Minton mod to the Carb. Darn, I love this bike. Perfect for the hilly twisties around here.
BatmanRon, you're scaring me. I'm getting an occasional fuel drip from under the accel pump. That little triangle cover, if I'm not mistaken, is to prevent the pump from pumping when the engine is turned off but I have no idea as to it's condition. As parts for these carbs are non-existant here except for some jets, I don't relish the idea of a new carb. Are any after market Carb parts available Down Under or in Oz? I'm leary of taking apart any more than I have to for fear of ripping a gasket/diaphram.
Anyway, I'll let you all know how it goes. Happy riding.
Bronson7
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Post by StewRoss on Apr 12, 2005 4:29:52 GMT -5
G'day,
There is another way out of all this pain. Get rid of the standard carby and put on a Mikuni, 34, 36 38.... easy change over and if you aren't good with jetting there are several kits out there to suit.
No more problems...the later standerd SR slide type carbs...well '80, '81, that's late here in Aus...besides being smaller, were not as good for some reason and they caused lots of problems from my experience. I put an earlier E model carby on my H model and that helped mine a bit.
I'm not sure what the newer CV type carbs are like to use...but they don't look too good...
While there may be a bit of adjusting jetting even on a kit, it'll be worth it in the end...and no more diaphragms!
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Post by Bronson7 on Apr 12, 2005 8:08:34 GMT -5
Point taken Stew, but those aftermarket carbs are a bit on the steep side. I should have everything I need for the carb when I get back to Kentucky. I ordered the diaphragms from the Yama dealer and a carb kit from the Bike Barn before I left.
Because of the leaking diaphragm(s), I've decided to do the .050" shave on the slide and thin out the needle spacer ('81 doesn't have the clip), replace the float needle/seat, gaskets and diapragms along with installing the stock exhaust as I'm almost positive the carb is stock. Once I know the carb is performing well, I'll change pipes and start the rejet project. After discovering the leaking diapragm, I started thinking that I could have chased my tail all over the country trying to rejet with other carb problems. Anyway, I'm looking forward to it. One more week till I get home. I sure miss riding my SR. Happy Riding.
Bronson7
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Post by canucksr on Apr 23, 2005 15:54:45 GMT -5
I am a new member and thought I would mention the carb I use on my 79 SR. It is a Mikuni from a TT500 that is gravity-fed. No vacuum is involved and you have to turn fuel on when you ride. The carb is much simpler than the stock SR carb and performs very well. The original carb gave me a lot of trouble (stalling, hard starting). My bike will pull strongly through all the gears up to about 90mph. I added a small in-line fuel filter to keep the works clean and am very satisfied with this set-up
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Post by Bronson7 on Apr 23, 2005 22:40:23 GMT -5
Canucksr, good idea but now I have everything I need carb wise, to do the job. Had an unfortunate turn of events today. I removed the Supertrapp exhaust in order to replace the clutch cover gasket and kick shaft seal thereby fixing an oil leak. I decided to hang the stock mufler in order to run it to see if I actually fixed the leak when I discover the stock exhaust won't fit. Must have gotten bent ( probably why the Supertrapp was on it). Anyway grabbed the Supertrapp only to discover it's cracked half way around about two inches from the header pipe. So now I'm looking for an exhaust system. When it rains, it pours. The weather's gorgeous and I'm stuck with my cage. Now, I'm leary to do anything with the carb until I find an exhaust. I'll get this licked yet. Happy riding.
Bronson7
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Post by G Man on Apr 23, 2005 23:26:17 GMT -5
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Post by canucksr on Apr 24, 2005 9:19:43 GMT -5
Hi Bronson, that sucks about your Supertrapp. Is it possible to have the crack welded? You need a welder who is good at stainless steel welding. I had the mounting bracket welded in place on two Supertrapps I have had.
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