Backfire at 4000 RMPS

[jtdlc10]

Going down the road the other day and boom the bike shuts off. now i was running low on fuel so i was alright but be out of gas got it to run adn limped it home notice it was running on one cylinder got home and to fine out there was still some fuel in the tank. (clean tank). so after that it would start back up, pulled the plugs and let it dry out since i thought it might be flooded. Go to start it later that day and it wouldnt rev past 4000 rmps and would backfire like western shooting a colt. So took the carbs off and cleaned them spotless notice the diaphrams where drenched in fuel so i swapped them with the "parts" carb i have, check jets all cleaned and clear. got it back on the fire and did the same thing. so at this point i checked the timing, and the cams themselves. everything was okay.  so im at a loss here NEED Help, want to go riding again.

[Blaine]

Have you checked the petcock for flow or dirt in the screens?

[jtdlc10]

Yeah flows great when vacuum is applied, and flows steady when on prime

[andyuk454ltdbiker]

hi, I am having the same kind of problem. I have stripped and replaced needles and all jets etc, setup what needed to be setup and i am still having the same results as before.

First of all my bike sat for about 5 months because of an illness so i was unable to ride, then what I was well again I ended up having to buy a new battery to replace the old one as it would not start. When I did get it running it would not go over 3k - 4k revs. So thinking it was a Carb issue, as nothing has changed within the last 12 months from when it was working perfectly I removed the Carb, cleaned everything, put new needles and everything changeable into it, made sure everything was clean, and then put it back on the bike.

Since then it has stayed the same. Checked the timing, rockers and everything but nothing has changed from the last service except for sitting for a while. Now I have read the forums and saw that it could be the filters, so I got myself some Pods, which did not make any difference, however the bike sounds better.

What happens is I start the bike up, let the chock warm the bike up, Chock goes up to 3k revs and I slowly back off the chock until the bike starts warming up. 

Once the bike is warm I disengage the chock, push it back, and give the bike a little rev up. I can take it to 3k revs if I slowly rev up but if I go from nothing to half throttle it dies or cuts out. I have plenty of fuel in the system, and I have no problem with tick over, but just giving it some gas and it seems to chock up. 

I have cleaned out everything and once I throttle back it will tick over at 1.2k which i have it set at.


Now I do have some questions. 

1, when the petrol tank is removed and the pipes are no longer on the bike, do you get flow of fuel from those pipes if, and i say if, you turn the fuel on (on the tank) or does it not drain out?

2, if it is suppose to flow, how would one dismantle the fuel system on the tank and can you get parts?

3 can this lead to the issue I am having?

[hounddog22642]

Just an off the wall thought, as I had the same problem wiith my '89 Honda PC800, have you checked the diaphrams in the upper part of the carbs? 
I had a very small hole in the right side and had the same problem you described. 
Good luck and please post when you cure the issue, I'm still working on my '88  454 and I do a lot of looking on here for advice as to problems I am having or may encounter.

[andyuk454ltdbiker]

I went and had my bike MOT'ed, Road worthy test in UK, today. Everything on the bike is perfectly good, and it passed with flying colours, however i did have issues with the bike misfiring and they changed the plugs, which made no difference. However as they are a good bike place they looked the bike over and came up with a few ideas.

1, setup the Carb once again, because I has one side which was running lean and the other side running rich.
2, track back the electrical system from the plugs back to the coils etc.

Here in the UK your bike has to have the Engine in a running condition and Road worthy. If the engine does not work its a fail, if anything is wrong with the bike it will fail.

I will track down the problem and post here what it is. At the moment I cannot pass 3k revs or go faster than 35 Mph. Its a little frustrating but I will get to the end of it.

Its remove the carb and set it up once again, but it is a shame there is just videos showing how to do it and its the first time I have setup a CV caeb, totally different to what I am used to.

Will keep you posted

[eaglerider]

There is a left side and right side wiring to the coils, and a positive and negative wire for each...make sure the coils are wired right.

[andyuk454ltdbiker]

OK, First of all I have found out that I am firing on just one cylinder, which is not good. 

Tested it by removing one spark plug and tested spark and at the same time tried to start the bike.

Left Spark plug in bike and bike started, and ran on one cylinder.
Right Spark plug in, bike would not start. 

Checking Carb to see if there is a fuel blockage on the right carb., so time to strip off everything and see whats going on. Luckily I have RamAir pods on which makes it easy to remove carb without taking of filters.

[andyuk454ltdbiker]

I have had to buy a new Carb which arrived today, have a little issue with it as I have water pipes that got to my old Car but the new carb does not have the fittings at all, should that worry me?

OK to my issue I found 2 major problems with my old carb.

1, the SCREW-PILOT AIR had broken so fuel was not coming through to one of my cylinders.

2, The NEEDLE JET holder, the thing with all the holes down had holes blocked up.

Now I could drill out the broken tip of the pilot air needle i do not want to damage the carb any more, and yes I have tried everything to get the tip out short of damaging the carb doing so, so i bought a new Carb.

Big test comes tomorrow when I fire up the bike for the first time in a few weeks. If it works then I have sorted out one issue. Next big job, riding on the road again whilst we are still in lock down (isolation is the correct meaning, ruddy News)