Cylinder 4 missing

Hey guys, it's been a while since I posted, but I've still been crawling around here. I finally started to catch a break at work and started working on the bike again (83 Spectre). I had been having issues with cylinder 4 before, so I took out and cleaned the carbs thoroughly, including running a little wire through all the passages and making sure carb cleaner would spray through. Got my float heights set, and got everything back on the bike, but cylinder 4 is still missing. I compression checked the bike last year when I first noticed the problem, and got 150-150-140-170. So the one missing is actually the one with the highest compression, but all of those are within the specified compression range.

I'm getting ready to send the head in for a complete valve job, and some welding that needs to be done on the exhaust side to fix where the PO overtorqued the exhaust. But before I do, I'm wondering if there are any other things you think might be causing the single cylinder miss. I'd hate to dump all the money on the machine work and parts and still not have a rideable bike.


I've thought about ignition, but it seems like if it was missing spark, there'd be two of them not firing, not sure on that one.

Oh, and I'm using the original airbox, exhaust, carbs. I don't 100% remember the jets from when I cleaned it, but I'm pretty sure they were stock.

Before you tear into it, diagnose that miss. Swap the coils from 1-4 to 2-3 etc. See if it moves. Is this miss just at Idle or through out the RPM range?

Del_Herring wrote: ...Got my float heights set....

If not already done, would verify fuel level by performing the clear tube test.

Good Fortune!

Yea, clear tube is how I set them. Just measuring was nowhere close.

I'll play with the coils when I get home. Need to get the brakes put back on before I try riding her, so I'm not sure if it's just at idle right now, but I'll try to get her going good enough to get it around the block in the next couple of days.

Could be a bad plug! If the coils don't change it, change the plug to a different cylinder or get a new one.

Ok, got a little work done this morning, and will try to do some more this afternoon. It's been torrential downpours here for the last week, but I think it's over for a while now. I realized I hadn't tightened the carb boots on the engine side when I put the carbs on, so I did that, which definitely made a difference overall, but didn't fix the misfire.

Took her around the block real quick, and she definitely seemed pretty lean. Had to leave full choke on the whole time, and once it was warmed up, it kept trying to idle high. If I took the choke down at all, it wouldn't take any throttle. Got her up to around 4000 rpms, but didn't get it too high since I don't feel comfortable taking it on the real road in this condition. 4th cylinder may have fired a couple times, there were a couple times when it felt like I suddenly got some extra power without having messed with anything, so it could be an intermittent spark problem.

Picked up some spark plugs/wires/caps yesterday, but they sold me the wrong plugs, and even after I told them I needed non-resistance plug boots, they sold me resistance ones right along-side the resistance plugs. So I'll have to go back and get that fixed on Tuesday.

I'll pull some plugs once the engine's cooled a bit and see if they yield any useful information.

I will get this bike riding properly again.

I'm having the same issue as well. I've checked fuel delivery from tank to carb on both fuel lines. (twin) Did a clear tube test. Have spark and the compression is in range. I just put new jets and everything in too. I can't figure this one out. I hope you figure yours out, and if you do let us know. Thank you.

Sounds a little vacuum leaky to me. Check the carbs and holders for vacuum leaks by spraying some WD-40 or starting fluid on the carb holders.

I JUST FIXED MY PROBLEM. Check your linkage between the pairs of carbs. I adjusted mine when I based it for a sync and then never thought to reset it.(month ago)haha i need to write this stuff down so I don't have to worry about forgetting stupid things.... Anyways, maybe the adjuster screw between carbs has come loose while riding and it has thrown that one cylinder off. Did the trick for me.

If I'm thinking about this correctly, you're just talking about the adjustment between the carbs that's used for syncing right? If so, they definitely aren't synced right now, but I'm thinking that shouldn't keep it from running when you're actually giving it throttle. It could definitely screw up the idle.

I have brand new carb boots from airbox to carb, so those are fine, but maybe the other side. I can try that. My airbox isn't in great condition, so it may be leaky as well. I can test that a little by just blocking it off some and seeing if that helps, shouldn't be too hard. I'll try spraying around the carbs a little too to make sure I'm not seeing any leaks there.

Yeah, the adjustment between the carbs. It fixed my problem. It might actually be firing at higher RPMs. The only way I knew that my dead cylinder was firing while rollong back was when I tried revving it with out the cap on that one spark plug. It made barely any difference, but it was just enough to notice that it actually was working. I basically adjusted the linkage between the two carbs to have the bad side's butterflies a little more open.