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Post by rustyrescue on Oct 21, 2022 22:02:05 GMT
work to recommission my 400n continues, it is coming along nice. I had it running super, carbs balanced, cleaned out etc. Now it is playing up on eft cylinder.....but it is not ignition it seems. Pull plug cap off with it running, no change in rpm and can hear the spark arcing to the plug if it is held close. It seems to stat on both pots using choke and drop out onto one...the exhausts both warm but then the left one drops out. I suspect carb, it has fuel in the bowl. Is there something in the carb that may be the culprit? slow running or something. I think I need carbs off again
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Post by BritPete on Oct 22, 2022 7:47:19 GMT
Have you tried to see what happens when you swap the HT leads
I think the SD uses wasted spark so that could eliminate coil HT issue
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Post by buster on Oct 22, 2022 7:50:43 GMT
lost the plot a bit with my own 400 carbs (had to rule them out of issues I was having) and took the pilot jets out to ensure that they were clean, not really recommended though. better to either keep going at them with carb cleaner and an airline or if your posh one of those ultrasonic cleaners. have you had the hidden jet out? its underneath the secondary main, needs a good fitting flat blade screwdriver. sounds a bit of an odd problem though, its not unusual for SD's to start on one and then both cylinders kick in, is the fuel feed into the float bowls completely clear? I'd also check the float itself, I put mine in a mug of water and gently weighted them down, then came back after 10 minutes to see if they took any water on board. might as well double check the float height while your there.
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Post by johnjones on Oct 22, 2022 8:07:46 GMT
Check valve working clearance.
Are the HT leads "wobbly" where they go into the HT coil ?
It's not a good idea to remove the HT lead from the plug when the engine is running, it's bad for the HT coil.
Yes, wasted spark system.
The safest way is to get a pair of those red HT plug caps but you will need to make an adapter so they will fit inline into the oe plug caps.
How are the plug caps by the way, resistance ok and no sign of HT tracking ?
Check valve clearances, and compression pressures when engine Is cold and when up to running Temp.
The left carb is the first to recieve fuel.
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Post by rustyrescue on Oct 22, 2022 10:06:57 GMT
thanks, so it has new coil, with HT leads. New plugs, switched caps around with many I have!! even other plugs. Valves set, new cam chain before I got it and checked it, compression good, carbs I took off and stripped/cleaned (have air line etc) I cant recall if I took out a hidden jet. Think I will pull them again (thats a mission wiggling them out from the gap!) but it was after initially cleaning carbs set up and idling lovely on both cylinders and balanced with gauges. The exhausts are currently off so will have another go when they are back on! they were missing the rubber seals I await delivery of which I assume slide over the joint and crimp with the clamp? they were blowing everywhere! haha
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Post by johnjones on Oct 22, 2022 11:20:57 GMT
Exhaust rubber seals ?
What did you set the valve working clearances to and what are they now ?
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Post by rustyrescue on Oct 22, 2022 12:23:54 GMT
valves were set to spec.....whatever the book said.From memory they were pretty good anyway in line with a bike shop having done the chain for previous owner. The rubber seals for down pipes and silencers to collector box. This has exhaust assembly paste all over the place but not sealing anything!
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Post by johnjones on Oct 22, 2022 13:44:50 GMT
That was then, check them now, 400 4 thou ex, 5 thou in, cold.
Just to rule them/that out else pulling hair out time.
Rubber seals, wire and graphite more like but hayhooo, we know what you mean.
The carb can be stripped down enough in site, dash pots off, float bowls off, float and needles out as well as most jets.
Be aware of slow running mixture screw arrangement, needle, spring, washer and tiny o ring.
That o ring can be problematic in that it sometimes refuses to come out, tips, and is buggered when needle assembly refitted.
I like to fit Allan bolts for the float bowl screws, makes life soooo much easier to remove float bowls with carbs in site.
I assume the tank has been flushed along with the fuel tap reserve "sump" that fills with crap/rust mud.
When cleaning tank don't forget the cap.
250 carbs don't have the economy/power diaphragm but 400 carbs do, the right carb being difficult, very difficult to get to the screws...
Illuminated possible causes with the carbs being last item/cause.
Enjoy.
Ps, have you shortened the left head steady bracket bolt on head to allow easier carb with inlet stubs attached carb removal method ?
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Post by johnjones on Oct 22, 2022 13:52:27 GMT
Yes, that deeply recessed jet is a real pita to remove. It has an emulsion tube with tiny holes.
I don't have an ultrasonic cleaner ( maybe Santa will bring me one ) so mix a strong solution of petrol and redex carb cleaner, enough to submerge carbs completely in a suitable container and leave for a few days. I clean the outside carp off first and strip carbs down. Liquid starts off cherryaid and comes out like coke.
By the way, your carb floats, black or white ( now orange ) type ?
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Post by rustyrescue on Oct 22, 2022 17:38:38 GMT
ok, I will go through it again. The carbs from memory were black floats, it currently runs in workshop off a remote clear bottle tank and a filter on the hose too. I wondered if it is the slow running circuit, starts on choke and as choke is turned off cuts out. I could try revving it harder to see if it comes on song again at higher revs. I have not tried doing the carbs in situ, done fist in my parts cleaner using and carb cleaner, airlines etc. Not seen the exhaust seals as not on it! assumed were like KH ones....rubbery! I think that little jet did come out, I remember the emulsion tube.....did them back in the summer so gone foggy on memory.
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Post by rustyrescue on Oct 24, 2022 14:12:24 GMT
the exhaust seals have arrived, now I see they are not soft/rubber as expected from other models. Having not had them the lovely new collector box fitted by lkast owner is a bit squishes at the joints.
Am I correct saying the graphite/metal seal slips onto the downpipe and the cans then has to insert into the collector box.
Then the clips crimp the collector box onto the seal.
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Post by BritPete on Oct 24, 2022 14:59:59 GMT
the exhaust seals have arrived, now I see they are not soft/rubber as expected from other models. Having not had them the lovely new collector box fitted by lkast owner is a bit squishes at the joints. Am I correct saying the graphite/metal seal slips onto the downpipe and the cans then has to insert into the collector box. Then the clips crimp the collector box onto the seal. Yes
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Post by rustyrescue on Oct 24, 2022 22:15:33 GMT
cool, I better reshape the collector box ends then! As an aside, my early kickstart 400N, would it have had chrome grab rails with the indicators fitted on the back of them?
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Post by buster on Oct 24, 2022 22:30:12 GMT
cool, I better reshape the collector box ends then! As an aside, my early kickstart 400N, would it have had chrome grab rails with the indicators fitted on the back of them? yep, hard to find good grab rails though I think the rubber mounts are available
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Post by rustyrescue on Oct 25, 2022 10:25:33 GMT
cool, I better reshape the collector box ends then! As an aside, my early kickstart 400N, would it have had chrome grab rails with the indicators fitted on the back of them? yep, hard to find good grab rails though I think the rubber mounts are available perfect, I have a slightly pitted but ok set and will fit them. I have the brackets and rubber indicator mounts too. I am baffled why they had rubber plugs in them (mine are missing) because with the indicators fitted the end of the rail does not show.
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