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1986 XV700 Front cylinder running rough (Single carburetor setup) (Connecticut)

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CoreyK250
Posts: 8
Joined: Sat Jul 16, 2022 10:26 pm
Location: Connecticut
What Virago you Own:

Re: Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by CoreyK250 » Sat Jul 23, 2022 5:43 pm

Alright I tested out everything today and it all went really good bike was idling good and would Rev up... Until it got warm that front cylinder started to pop and wouldn't stay running. I'm going to go back to my single carb conversion it has the same symptoms with the daul carbs.
My next plan is to get the bike hot and do all my testing when it starts to break up again.
Thinking it can be a bad pick coil getting to hot also curious if it could be the piston rings. If it was the rings wouldn't it have a problem at idle?

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faffi
Posts: 327
Joined: Wed Jun 08, 2022 9:55 am
Location: Norge
What Virago you Own: 1982 XV750 with XV1100 engine, Seca rear wheel, XT600Z shock, Seca 650 fuel tank

Re: Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by faffi » Sat Jul 23, 2022 5:55 pm

I would be very surprised if it is caused by engine wear. Maybe, but unlikely, inlet valve with no clearance. More likely something concerning spark.
The journey of a thousand miles begins with a motorcycle.

CoreyK250
Posts: 8
Joined: Sat Jul 16, 2022 10:26 pm
Location: Connecticut
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Re: Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by CoreyK250 » Sun Jul 31, 2022 11:11 am

faffi wrote:
Sat Jul 23, 2022 5:55 pm
I would be very surprised if it is caused by engine wear. Maybe, but unlikely, inlet valve with no clearance. More likely something concerning spark.
Hey sorry for the late response been busy with work.
Alright so I was thinking it was engine wear as well maybe piston rings but I've replaced the front jug with a nice looking one and a different piston plus the rings. I didn't check them when I installed it just did a visual check for wear or scratches. Still had the same problem I have another camshaft so I'm going to pull this one and swap the two.
I also did a leak down test on both cylinders I preset the gauge to zero before using it. I then put each piston at top dead center hooked the gauge up and it's below 10% on both cylinders. Front 5% rear 7% I pulled the fill plug for oil and I can hear a little bit of hissing almost like it's blowing by the rings. Both cylinders are in the same range so I can't see it being exhaust or intake valve there's no hissing coming from the intake or exhaust.
I also replaced the pulse coil and no change the rear cylinder runs amazing I just don't get why the front is miss firing and dies when I do the drop test.
Any other ideas on what I should check next?

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faffi
Posts: 327
Joined: Wed Jun 08, 2022 9:55 am
Location: Norge
What Virago you Own: 1982 XV750 with XV1100 engine, Seca rear wheel, XT600Z shock, Seca 650 fuel tank

Re: Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by faffi » Sun Jul 31, 2022 4:12 pm

Personally, I am where I started - that the issue is most likely with the single carb. The only confusing part is that it runs more or less the same with the stock setup. So these are the tings I would check:

Spark. Use a strobe timing light to see if spark is reliable. I know you have done much here, but that is what I would do.

Cam timing. Could it be off on one cylinder?

TCI unit. It could perhaps be bad for one cylinder only.
The journey of a thousand miles begins with a motorcycle.

CoreyK250
Posts: 8
Joined: Sat Jul 16, 2022 10:26 pm
Location: Connecticut
What Virago you Own:

Re: 1986 XV700 Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by CoreyK250 » Thu Sep 08, 2022 3:15 pm

Hey everyone! Just wanted to post a update on what I've been doing to my Virago.
I ended up removing the single carburetor setup it just wasn't working for my xv700. I went a different route and adapted a single Mikuni vm30 to each intake manifold. I started off with one carburetor and tuned it to run perfect on the rear cylinder then swapped it to the front cylinder. That didn't end up working I needed to make a adjustment to the carburetor pilot jet to make it run. I thought this was strange why I had to change the jet size for it to run?? Long story short the rear cylinder was having issues I had a leaky intake valve not sealing properly.
So I swapped a low mile cylinder jug in also new pistons rings and a different cylinder head I re-used the old camshaft out of my head that came off. I swapped the carb over to the rear and long behold it ran just like the front did!

This is where I decided to try the single carburetor intake again with the perfectly tuned carb for both cylinder's. Bolted everything on and tried to start it the bike ran like crap. I figured the jetting was off cause I had it set up to run a single cylinder not both at the same time. So I swapped in a 40.0 Pilot jet Ran the 6f5 jet needle on the 3rd clip down and left the main jet. I still couldn't get this bike to run right at this point I think this cheap manifold I bought was just garbage.
I rushed to Evil-Bay and purchased myself another Mikuni vm-30 and a universal dual throttle cable this works for now but later I'm going to change this cable where the 2 cables meet is a big metal coupler and it sits right on my horn and looks horrible but it works for now that's all that matters for testing.
The cable I bought was a DUAL CABLE 924 For Mikuni.

I'm still working on finding intake boots that work perfect for the 30mm bore on the carb and trying to find a flange that fits the bolt holes on the heads. I think I came up with something but waiting for parts to get here still for now I'm using old radiator hose to fill in the gap on the manifolds for the original carbs to the 30mm bore on the new one just for testing not a permanent thing.
I bolted everything together and noticed the idle screws are on the inside of the carburetors so this will be a pain to sync the carbs but its doable.
For the throttle cable I needed to go wide open throttle to set the round slides to open and close at the same time. I did this with my finger I opened the throttle all the way and made my adjustment to one side then locked the bolts down. I then felt with my finger where the slide was sitting at the top then made adjustment to the other carburetor till it felt the same then locked it down.
I preset the other carburetor to match the one I had running perfect for the front before going onto starting the bike up. I then fired it up and the bike came to life at this point it needed tuning I did the pilot jets first the 40.0 that comes with the carb is to big for my application so I put 15.0 for the front and 17.5 for the rear. After swapping new plugs in and testing the idle I was happy with the nice Carmel color for both spark plugs.
I moved up to test riding I took it down the road and it just popped and sputtered the whole time so I pushed it back to my driveway and adjusted the jet needle one clip at a time. I ended up maxing these out I may need to look into getting different needles seeing its maxed out and will probably need to go a little further up.

It was time for another ride after maxing the needle jet all the way I got on the bike put on my helmet then pulled out of my driveway. The bike started going and it was snappy too! I gave it a little gas and it started pulling pretty hard no bogging or sputtering it just took off.
This is it! I was actually able to ride the bike! I was so happy my hearts racing I'm all shaky I have the biggest smile on my face cause all I wanted this whole time was to ride my motorcycle and I was finally able to do that! After all the countless hours I put into this bike and fighting issue after issue I was able to just feel the wind on my body and the feeling of actually accomplishing something after spending so long much time on this bike.

This is as far as I got guys the bike still runs good I do need to order more parts and tune it a little more to make it 100% but for now I'm able to ride it and I'm happy.
For air cleaner I did end up going to Lowes and buying some pvc rubber couplers 2.41in and cut it in half. I bought some exhaust tube that fit inside the rubber boot for the intake side of the old carbs and I hose clamped the hose down onto it to extend it and fit my new carbs. I then bolted my old air intake box onto the bike and it looks and sound good really happy I went this route.

I wish I could of figured out how to get that single carb intake to work but I'm happier with running two Mikuni vm-30's and being able to use my factory intake. Thanks again faffi and everyone else for your help!!

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jsyzdek
Posts: 290
Joined: Mon Feb 17, 2020 5:31 pm
Location: Oakland CA
What Virago you Own: 1995 XV1100. My dad has a 1996 XV535. I also ride a 2008 SV650S and 2004 Yamaha TTR125. Currently restoring a 50cc Yamaha Champ moped

Re: 1986 XV700 Front cylinder running rough (Single carburetor setup) (Connecticut)

Post by jsyzdek » Thu Sep 08, 2022 4:35 pm

That's AWESOME. Wrenching on the bike can be quite satisfying, but the primary reason most of us get these is to ride them. I'm glad you're able to do just that.
Keep Calm and Ride On!

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