Virago 750 won't run. Video.

Hey guys. I have been working on this bike (1982 Virago 750) for a long time now and I haven't been able to run it. I tried everything and I am putting a video here to see if anyone can help me with this sphinx mystery.

Things i have done:

1) New pistons and rings (from a 97 VIrago - compatible)
2) New cylinder and head gaskets
3) Compression at front 120 psi, rear 110 psi (cold test)
4) New spark plugs - have spark and they look quite blue
5) Timing done as specified (crankcase at T and rear cam at 0 degrees, crankcase at I and front cam at 0 degrees and rear at 142 degrees).
6) The coils wires are correctly connected (orange and gray).

As you can see in the video

https://www.youtube.com/watch?v=ZsKIssE_V9k&feature=youtu.be

there are explosions in the cylinder and fire coming out of the exhaust (fire bc I am using starting fluid).
However, when the explosion happens, the starting motor can't keep pushing it - on the video on seconds 6 and 8 you can see the explosion and the easing of the starting motor.



I appreciate all the help . This forum has helped me with so much already!

After cranking it over like that in the video, are the plugs wet? Generally if they are wet after cranking, you have a timing issue. I am not familiar with this engine, but you neorro example.

Just a note, Quick Start and its equivalents are designed for Deisel engines. I would not be using it too much in a gas engine as it can burn a hole through pistons beacuse it burns so hot.

STOP USING THE STARTING FLUID!!!!! There is no situation WHATSOEVER where it will benefit you unless you are looking for intake leaks and know what you are doing. I have personally seen PERFECTLY GOOD ENGINES completely destroyed using it.

Check things methodically one at a time and KNOW they are ok. You have spark, so make sure it occurs at the right time. Many engines can be put together with the ignition 360 degrees out, so be certain of the compression stroke. If you don't have a way of checking the timing without the engine running, estimate it as close to top center as you can - most will start and run quite easily with little or no advance.

Looks like you have enough cold compression for that to not be the issue, but check the valve train and lash if for no other reason than to know it is good.

Double check the coil wiring - many bikes are easy to have backward. High voltage leads as well.

Once you are certain the ignition is correct, see if you can start it with new plugs. Check the plugs for gas. If they are dry, go to the carbs. If wet, figure out why - either the carbs have issues or the ignition does.

Engines in good condition generally start very easily. Rebuilt or new engines ALWAYS start VERY easily unless there is a problem and it is almost always something obvious, major or silly. Small nuance adjustments almost never come into play, so stay focused on the basics. Never use starting fluid or pour gasoline into your engine. Neither will help you find the real problem and the risks are great.

Yeah, I would check the coil wiring too.

Thanks for the replies.

This engine has a TCI to time the firing of the spark plugs. I don't know if there is a way to check if the TCI is firing at the right time though.

I read somewhere that rebuild engines might need a very good battery, some people even try to use a car battery in the beggining. I constantly recharge mine but maybe it is too weak/old to run it?

I quit using the starting fluid for now. I will try again with gas today, but now I have to worry about the carbs also. I will run and check the plugs for gas. The plugs are also brand new.

So I checked again and the spark plugs comes totally dry after trying to crank it. I can see also that there is fuel being sucked inside the carbs bc I have transparent tubes from the peatcock to the carb and they are full.

I rebuilt the carbs, with new needles on both and cleaning with carb fluid. Not sure how to proceed now.

So are the Valves opeiong at the right time with the piston. you can only "suck" if the valve is open. the small puffs of ignition seem to indicate hat youa re getting a "bit" of gas.

float level? jets?

throttle?

choke?

is there fuel in the bowls?

is there an overflow tube to check?

Using a car battery is not a bad idea, but your bike sounds like it is spinning fast enough to start. Your video seems like spark is not happening at the right time so I would first eliminate that. Since you have obvious spark, take out the plugs and rotate the engine by hand and rotate the engine so it stops just when a plug fires. You may have to use the starter motor and estimate it because you may not get a spark rotating the engine slowly by hand. Once you have that nailed down, verify that at this crank position the piston for that cylinder is at the correct place. The correct place is slightly before top center on the compression stroke. Check that the other cylinder does the same thing. The idea here is to have confidence that the timing is close enough to work, not that it is exactly right. If you can get spark when turning by hand, and they happen right as you come up to top center on the compression stroke you are good and you can focus on the carbs.

Rebuilding a carb means 100% disassembly (only exception are swagged in balls that permanently seal off drillings)and understanding what every passageway and drilling does so you can tell if it is working. If you have not done this, you don't know if the carbs have issues. Generally, unless they were left full of fuel for a long time (weeks) and if they worked ok when removed from the bike, they will likely work the same when put back on. I rarely replace anything in carbs except seals, and almost never buy a rebuild "kit". Beware of using "kit" parts - they are often of inferior quality compared to the used parts you already have. The last rebuild "kits" I bought were for some Bing carbs on a BMW because they have a bunch of o-rings for seals. Gaskets, o-rings and shaft seals: buy them separately and you are better off.

In my experience you can very rarely tell a carb has some specific problem by running the engine. If the bowls overflow, that is pretty obvious, but most other things get solved by a complete cleaning and sealing as opposed to "I know the problem, there is a restriction in this passageway, so I will fix that and all will be well". Everything in a carb overlaps something else so problems mostly are not obvious until you do a comprehensive disassembly and cleaning.

Right now, I expect your issue is ignition. The reason is that if the cam timing and valve lash is ok, and the spark timing were ok, your engine should have very obviously tried to start with the starting fluid (assuming it didn't get instantly destroyed). If everything is good except the carbs, you likely would have got a brief start on the starting fluid, but no continuation of running due to the carbs not working. Since you got nothing at all, either there is another more major problem or the timing is way off.

Good news.

I put new gas on the tank and tried cranking it. I saw that there was something going wrong on the carbs. There was no gas flowing from it. So i took it apart again and checked the needles and floaters, rebuild it and put it on the bike.

Tried to crank it again and it fired up on both cylinders, not running though. It was a succession of explosions, leading to a black smoke (probably bc of the choke). It didn't start running though, it was only a sequence of blows and weak explosions while the starting button was being pressed.

Battery is charging now. Any ideas how to make it run continuously?

Timing

Pull off the plug caps to either front or rear cylinder. Does it run any better?

Good news!

I quit using the starting fluid and put work on making sure all the parts were fine.

First the wiring was a little messy and the starting was moving slow. So I cleaned the ground and the plugs with the battery. I am also using a car battery, which is new.

Second, the vacuum line was redone, with new pipes.

Third, I opened the carbs again and put back the original float needles and checked the floating balls.

After doing it all, the engine works! it is not really idling, but it runs and stay on for a while. If i play with the choke it stays for longer, but as soon as I let it go, it stops.

Overall, problem solved, moving to the next one. Thanks everyone that helped me with all. Really appreciate it.
:thanks: