Bob H
New Member
Posts: 9
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Post by Bob H on Aug 29, 2008 1:13:49 GMT -5
I have a 78 SR500E with stock VM34 carb, white Bros pipe with supertrapp, K&N air filter rest of engine is stock... When going from decel to accelerating there is a momentary "bog" before the bike pulls nicely... same thing off idle at a stop, very slight hiccup and then it runs great, I think i'm pretty close but was wondering what this might be - too large of a pilot jet? needle need to drop one? I don't want to make any big changes... what about the air screw - which way to loean it a little? thanks for your help...
Bob
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pcnsd
Full Member
Posts: 113
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Post by pcnsd on Aug 29, 2008 20:29:01 GMT -5
Turn clockwise to richen, counterclockwise to lean. Typical adjustment is somewhere between 1.5 and 3 turns. You can test for which condition is present.
Does the condition get worse when the bike warms up? (Too rich)
Does the condition get better with the choke on? (Too lean.)
On another thought, Is your gas good (fresh) or has the bike been in storage? You may just need to clean the carb.
Good luck, I am sure others will have some input also.
PC
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Post by wotavidone on Sept 1, 2008 19:30:28 GMT -5
At the risk of being called a slapper, I'll put forward this suggestion.
Have you check the adjustment/freeplay on your throttle cables?
Mick
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Bob H
New Member
Posts: 9
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Post by Bob H on Sept 1, 2008 19:46:51 GMT -5
not sure what a "slapper" is, but if i knew you better i might have to slap you for asking that..... it's not the cables, it's the carb.... but thanks
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Post by wotavidone on Sept 1, 2008 21:21:16 GMT -5
 I reckon you've got a reasonable handle on what to do with a slapper. I'll take it this means there is not a massive amount of freeplay in your throttle cables. |
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Post by miker on Sept 2, 2008 14:18:54 GMT -5
Reading the Minton article, isn't this off-idle bog what trimming down the slide cutaway was supposed to fix?
miker
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cliff
Junior Member
Posts: 42
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Post by cliff on Sept 2, 2008 17:06:56 GMT -5
The Minton Mods fix this bog.
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emil
New Member
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Post by emil on Sept 3, 2008 16:11:37 GMT -5
...so does the stock air filter. I have a straight pipe, completely stock carb, and a stock air filter. My SR runs beautifully. I had the K&N and the the exact same hesitation as you. After countless jet changes it seemed the only thing left was that slide-shave the Minton mods suggest. I wasn't quite willing and so just for kicks I threw in a stock filter. The bike runs perfect. I know the stock filter isn't fashionable but it works, highway and street.
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jeffz
Full Member
Posts: 215
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Post by jeffz on Sept 4, 2008 12:23:57 GMT -5
I also had the same problem, but after I switched to a XT carb, it fixed it. Same jetting and needle position. Not sure why it made a difference but I'm happy with it.
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emil
New Member
Posts: 20
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Post by emil on Sept 30, 2008 22:12:36 GMT -5
I have to amend my earlier post. I had to switch mufflers and while I thought my previous muffler was straight thru it was not, hence the performance with the stock air filter. I put on a muffler that was truly straight thru and yes, I had to switch back to the KN filter. With some pretty academic tuning on the carb tho, per the maunal, not the minton mods, I had the muffler running well, ie, without the hesition.
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Post by 5twins on Nov 1, 2008 9:48:57 GMT -5
I had a similar problem with the stock 34mm carb on my early '78. Turned out to be the accelerator pump. Apparently it was set wrong from the factory and was pumping too much, creating an overly rich condition just off idle. The cure was simply to disable it - pull the cotter pin from the rod that connects to the pump arm. There is a small washer or 2 that will come off the bottom of the rod when you pull the cotter pin but all other parts will stay in place, the arm won't be moved anymore and the pump won't pump. There are several holes through the rod for the cotter pin so note which one was being used in case you need to reinstall things.
This is worth checking because that rich condition can carbon your top end up. On mine, at about 7K, I lost compression and had to rebuild it. The top of the piston was all carboned up and the carbon had crept down the sides and stuck the top ring in it's groove. The valves and valve seats were also all carboned up and leaked like crazy.
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I reckon you've got a reasonable handle on what to do with a slapper. I'll take it this means there is not a massive amount of freeplay in your throttle cables.
