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Here we go "AGAIN"

13K views 194 replies 9 participants last post by  Will750 
#1 ·
As most of you know this bike has given me trouble right from the get go. Recently it was taken apart for some repairs(coolant in the oil) so i split the cases to give it a good clean and make sure everything was in tip top shape. New mech seal , new gaskets all round etc. I had it running before i took it apart so this has left me stumped. Right here goes. Went to start the bike after the rebuild and nothing. Cranks and cranks with the odd shotgun bang 😁 ( scares the **** outta me everytime). But no start. Battery is brand new mf battery, timing is spot on 305* as i wont make the same mistake twice. Everything lines up with all the marks. Starter is perfect. Good blue spark from the plugs. My carbs do need a little work (float stuck i think) but there is fuel in the bowls after i prime them. Here the funny part. After cranking the plugs still look dry. So next step. Try starter fluid. Few squirts of starter fluid and still nothing. Anyone any ideas why it wont start. Im at my withs end with this bike. Im at the stage of just getting rid of it. Any help much appreciated.
 
#3 ·
the bike has the ear shave done to her. So get this. Just went out. Took tank off last night and drained the bowls. Sprayed starter fluid into it and she ran for about a second. Put a small bit of fuel in the bowls, gave it a shot of starter fluid and she fired up. But only with full choke and full throttle. Even then it sounded like she was bogging down. Any ideas what could cause this. Im lost to be honest. But at least it ran even if it was bogging
 
#10 ·
Ok so a range of new problems arised. Got the bike starting first push of the button after i squeeky cleaned the carbs. Now the bloddy thing wont rev passed 2k. It started by firing only on the rear cylinder but once i got this sorted and running it startrd popping like crazy. I also noticed that the vacuum slides are vibrating like crazy. I have a leaky petcock but even with the tank off and just the fuel in the bowls it does the same. It idles fine for a bit but if i even look at the throttle is dies. Any one any ideas?
 
#14 ·
No thats one thing i dont have. I doubt its the valves as they were lapped during the rebuild. The first time lol. I will have to thinker with it again. I might switch slides and see if that makes a difference. I could have mixed them up when i took them apart. Not sure if that would make a difference or not tho
 
#21 ·
The slides are vibrating rapidly as in up and down motion. When i twist the throttle the slided move as they should but the carbs are spitting fuel and popping. Anywhere near 2k and it hesitates and dies. Im waiting for a new rebuild kit for the carbs but it just dont add up. I made sure they were squeeky clean before i put them on so the jets cant be blocked
 
#22 · (Edited)
Try it with the air filters installed?

Some reversion (spitting gas back out intake side) can be normal, but an excessive amount combined with the right sort of popping, can mean a leaking intake valve.

Compression test? Air test?
 
#23 ·
comperssion is good so im thinking air myself. I was thinking about it last night and the only thing that was different with the carbs was when i was cleaning them the 2 tiny o rings that are at the base of the air/fuel mixture screw came out. Im just wondering if they somehow managed to twist a bit going back in. Slightly blockinging the air/fuel ratio
 
#24 ·
Again, the slides move up and down in sync with the intake stroke of the cylinder that carb supplies. this is normal. more throttle will cause them to open more on each stroke.

you may have an issue with the carbs still, I am just pointing out the pulsing of the slides is normal.

if they didnt pulse, I would look at the slides, diaphrams, or other vacuum issue in the carb
 
#25 · (Edited)
I don't think the air adjustment is going to cause all those symptoms so far above idle rpm.

By air test, I meant similar to a leakdown test, pressurizing the cylinder and see if there's any air where it shouldn't be, as with a leaking intake valve.

Won't hurt to check those o-rings, an internal air leak can only cause a problem. We could be looking at overlapping symptoms.

When does the popping occur? All the time, only above 2000 rpm, or only right before it dies? Or is it random?
 
#26 · (Edited)
It happens all the time. I cant touch the throttle or it will bog and instantly die. Right so here is what im doing. Iv ordered a fuel tap rebuild kit, carb rebuild kit. Im putting back on the surge tank and stock air filters. Leaving the emmisions crap off. Its deffo a carb problem because after the engine rebuild it would not fire as you no and once i cleaned the carbs it started first pick only now there is the current problem. I just pulled the jet cover and on the front carb the little triangular shaped rubber gasket was broke. Still together but just sliced if you get me. Could this have caused the problem. Also thanks mishiganteddybear. I get what you mean about the slides.
 
#28 ·
Spockster thank you for all your input. Iv just ordered a gauge so should be here hopefully by the end of the week. Have some bits ordered so all will get done regardless. Just hope that i dont got to pull the engine again for a valve job. I will keep this thread posted for future references.
 
#29 · (Edited)
You're welcome, hope I'm not sending you on a wild goose chase. The answer to that question earlier was yes, correct ?

Pulled my engine twice in two days because I goofed installing the damper gear. I really wanted that first ride.

Second time was easier, quicker.

Where did you find the gauge? Was about to remove the one from the dash of my pickup, all my toolbox gauges are too old to use.

Look up some charts online for vacuum readings, will help with troubleshooting other engines. Though I've seen one or two that didn't jibe with printed manuals. Almost all Chilton, Haynes, Clymer automotive manuals have the chart in the troubleshooting section.

One of the vac gauge's best uses is checking for valve problems ... Oh and clogged Cats too.
 
#30 ·
yes to the question earlier. Iv order one from motorcycle shop here in ireland so it should be right. I have the haynes manual so i will have a look in it for the specs. Iv pulled this engine more times than id like to say. Put it this way. 15 mins for an engine pull and 5 mins for carbs. Im sure i could take the engine apart at this stage witj my eyes closed lol. I think this time tho if it is the valves of something like that im just gonna send her to a mechanic and get it back when its ready to ride. I no it runs so thats the main thing. If it didnt run i would have just parted it out. Time will tell. Lets hope its an easy fix like something i over looked.🤞. On the other hand once i find the problem it should help anyone else that runs into this situation.
 
#31 ·
Pretty good time for an engine pull!

You could verify the valve is leaking with an air pressure test. Need compressed air and a fitting that will thread into a spark plug hole.

You put air pressure into a cylinder, rotate crank to where all valves are closed, TDC of compression stroke, then listen for air escaping intake or exhaust.

Once the head is removed, you can fill the areas behind each valve with liquid to see if it leaks into the combustion chamber over time. Liquid like gasoline, alcohol, or probably even water.
 
#32 ·
yeh i seen some videos on valve leak test with fuel. The head was off the bike tho. Not sure if it could be done on the bike. Altho im sure if you could see the valve ports you might have some hope. Pretty neat idea with the air test. I might give that ago while i am waiting for my gauge to come
 
#34 ·
Problem found. This is definatly one for the record books. Ok so pulled the carbs again to take a look. Pulled the jets from both sides and low and behold the main jets are screwed. I obviously seriously over tightened them. In my defence.. ok i dont have any im an idiot lol. Judge for yourself by the pics. I await your roasting 😂
 

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#35 ·
While that's not good, I'm struggling to figure out how that would cause constant popping from one carb. A lean sneeze if fuel doesn't flow well, but only when the throttle is opened and just one pop.

Might check to see if the carb body is cracked near the jet holes.

Don't be too hard on yourself, this is one of ways we can learn.
 
#43 ·
Ok so recent update:
Lots done to find the problem. Carbs rebuilt. All new gaskets, jets etc.
Compression check: Ok
Fuel tap rebuilt.
New plugs.
Valve check: Problem with front cylinder.
So far this is what was wrong. Opened the cylinder cover and cam cover. Took off the tensioners and removed cams. ( making sure it was tdc and marks aligned. (Turned engine by hand)
2 of the cam guides that sit on the lash adjusters had fallen off. It must have happened when i put the cams on the first time without me realising. So spockster you were right about the valves.
I have yet to fire it up as it was late last night when i finished putting it back together. The whole procedure was done with the engine on the bike. Took about an hour in total. I will post the outcome later.
 
#45 ·
Yes only on the front. Was a bit tricky but i managed it. So went to start the bike today after work and nothing. Eventualy got it to run with a shot of starter fluid. It idled great on both cylinders but i was still not able to rev past 2k or it would bog and die. Lots of popping and backfiring. I wonder would it have anything to do with the exhaust system maybe? I have the gb removed so pipes are just straight from the head to the rear mufflers. Its all i can think of as im out of options. I think its time to bin this engine and try and find a replacment as my paitence have worn out with this one. Any last ideas before she goes for the scrap heap?
 
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