View Full Version : Poor running on front cylinder - Curvy.
My sv650x has never quite run right; when cold it most often starts just on the rear cylinder, with the front randomly kicking in. Once warm it runs better, though still a little rough, and it's been noted the exhaust gas is pretty hot.
With air filter off, covering the rear carb with hand causes the bike to stall, doing the same with the front carb causes it to idle slightly higher.
Spark plugs look like so (front on right):
https://dl.dropboxusercontent.com/u/10861049/sv650.org/20130521_185338.jpg
So far I have:
Checked choke plungers
New plugs
Carbs stripped, cleaned and balanced (Thanks Bibio!)
Coil resistance checked (5 ohms primary, 27 k ohms secondary - same values on both coils)
Redex applied
Compression checked (14.7 bar rear, 14.4 bar front)
Swapped the current spark plugs over
Nothing has made a difference so far, what's left to try?
From what you say, sound like it's running far too lean on the front carb (putting your hand over the carb intake works like a traditional choke and makes it run rich). This suggests a possible air leak or maybe a blocked idle jet.
Check the carb is sitting in its rubber correctly, the clip is tightened properly, the rubber isn't split, and the cap isn't missing off the vacuum tapping used for balancing (front right hand side of inlet stub).
If all these are OK, it may be an idle jet blocked, which really means dismantling the carbs to get to it for blowing through and washing out any crud.
The plug can look like that if it's only firing intermittently, fuel builds up making it wet and cold, then it fires and makes it grubby.
Surely what youve just listed wouldnt be an issue if hes just had the carbs cleaned?
OK
Thankfully I had no tea in my mouth as I read that!
"Cleaned carbs" can mean different things to different people. The compression check suggests everything is ok mechanically, so fuel is the most likely culprit. I'd run with embee on this if I were you, his logic is always very sound, and he knows a thing or two about motors and SVs.
If you're uncertain a simple check can be to substitute in a known good bank of carbs from a clean running bike. If the problem persists (and the other checks mentioned by embee don't turn up anything obvious) report back :-)
Jambo
Sent from my thingie
Wasnt being rude, just checking you hadnt missed that on the op.
wideguy
21-05-13, 10:17 PM
I spent a long time working on airplanes, and the most logical thing to do to diagnose a problem was to check to see what had been worked on lately. This was often where the problem was.
Everybody hopes to fix things when we work on them, but most everybody sometime or another, makes things worse.
I'll try and get the carbs off tonight and check the seats. If they all look OK and I end up stripping the carbs is it just the idle jet worth looking at?
wideguy
24-05-13, 01:02 PM
I'll try and get the carbs off tonight and check the seats. If they all look OK and I end up stripping the carbs is it just the idle jet worth looking at?
Did you do what embee suggested and make sure you had no vacuum leaks into the front cylinder?
Any time the carbs are removed, there's a chance they won't properly seal into the intake boots on re-installation.
It's worth looking at the idle jet, but only after you are positive you have no vacuum leaks.
Bagpuss
24-05-13, 05:59 PM
I spent a long time working on airplanes, and the most logical thing to do to diagnose a problem was to check to see what had been worked on lately. This was often where the problem was.
Everybody hopes to fix things when we work on them, but most everybody sometime or another, makes things worse.
Remind me not to get on a plane you've worked on then :)
andrewsmith
24-05-13, 07:36 PM
Start at the carbs and the rubbers.
Smear a tiny bit of RRG around the rubbers helps them seat better. When you put the airbox on, take the filter out and offer it and work them properly from the inside.
Check the fuel lines aren't kinked also.
Going to put the one Rictus suggested to me with the crap running. Clean up the coil connections and blast the HT end with contact cleaner or change it, then apply Vaseline to the coil pack ends
wideguy
24-05-13, 09:26 PM
Remind me not to get on a plane you've worked on then :)
Why would you say that? Have you been lucky enough to always find mechanics who quickly and accurately diagnosed problems, then fixed them, properly?
I've run into mechanics like that, quite a few of them, but I've also run into a lot that made things worse, or caused some new problem as they repaired the original problem.
I learned, when you hear "I just replaced/cleaned/repaired" some part of a mechanical device, and a different problem has suddenly appeared, the best place to start looking is with what was repaired or replaced.
That's just a simple good sense lesson.
As to my actual mechanical skills, you know absolutely nothing.
Check the carb is sitting in its rubber correctly, the clip is tightened properly, the rubber isn't split, and the cap isn't missing off the vacuum tapping used for balancing (front right hand side of inlet stub).
Seemed to be sitting fine, and clip tight. Rubber of the duct feels OK too - I don't really want to try and remove it to examine better as screws don't feel like they going to go - unless I need to take them out?
Did you do what embee suggested and make sure you had no vacuum leaks into the front cylinder?
Any time the carbs are removed, there's a chance they won't properly seal into the intake boots on re-installation.
It's worth looking at the idle jet, but only after you are positive you have no vacuum leaks.
Yep. Checked as best I could with them in place then removed the carbs to check the ducts. Is it worth sticking them back in again to rule out a bad seal before trying to strip the carbs?
Start at the carbs and the rubbers.
Smear a tiny bit of RRG around the rubbers helps them seat better. When you put the airbox on, take the filter out and offer it and work them properly from the inside.
Check the fuel lines aren't kinked also.
Going to put the one Rictus suggested to me with the crap running. Clean up the coil connections and blast the HT end with contact cleaner or change it, then apply Vaseline to the coil pack ends
Will grab some contact cleaner tomorrow and, as above, try all this before stripping the carbs.
while you have the carbs out check the pilot screws to make sure i set them again after cleaning.
ooohhh and he forgot to mention the bike cuts in and out of 2 cylinders when heated up. i also noticed that the exhaust gasses where very very hot.
andrewsmith
25-05-13, 09:01 PM
while you have the carbs out check the pilot screws to make sure i set them again after cleaning.
ooohhh and he forgot to mention the bike cuts in and out of 2 cylinders when heated up. i also noticed that the exhaust gasses where very very hot.
Fuel or coils by the sounds of that
while you have the carbs out check the pilot screws to make sure i set them again after cleaning.
Wildo. What do I check they are set to?
ooohhh and he forgot to mention the bike cuts in and out of 2 cylinders when heated up. i also noticed that the exhaust gasses where very very hot.
Good point. Cold and at idle the engine runs mostly on 1 cylinder, with the second occasionally kicking in. Warm at idle engine runs mostly on 2 with the occasional drop to 1. Cold with a bit of throttle, runs on both.
what book says. it's something like all the way in and 1/&1/4 out but the book will say. i dont have the mk1 manual to hand so don't know the turns.
what book says. it's something like all the way in and 1/&1/4 out but the book will say. i dont have the mk1 manual to hand so don't know the turns.
Book says 2 1/2. Rear was 2 1/4, front was 1.
I'm still going to clean up connections but will put the carbs back in without stripping as presumably that could be the problem?
andrewsmith
26-05-13, 02:12 PM
Test it
That wont help tbh!
sent from a weapon of mass distraction
Well, after adjusting the pilot screws and cleaning the contacts, it does seem a bit better. It's still not quite right and was threatening to cut out, but didn't, and the choke works more like it should.
This close to the GM I'm going to stop mucking about with it in case I properly break it. Once I'm back I'll try and adjust the pilot screws with the carbs in place - do you need a special tool? If that still doesn't sort it I'll strip the carbs again.
andrewsmith
27-05-13, 05:52 PM
Neil
Check the clamps and replace the screws if you can. Mine were bad when me and Berlin disturbed them
Well finally got round to getting hold of another set of carbs and that seems to have sorted it. Only part fitted them but the bike started almost immediately and sounds much better. Will fit them properly tomorrow and go out for a run to see how it is once warmed up. Quite chuffed as it's not seemed right since I first got it. Might even celebrate with a new can.
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