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Smoking on startup

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So, I pulled the head off this weekend and changed the valve seals. You could see some oil on the exhaust stems so I was confident that the seals would fix it. Put it all back together and it still smokes on startup. Not just a little smoke, its a pretty good fog. It takes about 20-30 seconds to start smoking and then it fogs pretty good for about a minute or two and starts to taper off. Smokes all gone within 4-5 minutes. I guess I should have ordered some rings while I was at it. I already checked the vent hose it does not have any kinks or squeezed shut. Anybody got any ideas other than rings? It didn't smoke last fall, I tore it down for a color change get rid of purple and it has smoked since I put it back together. It smokes bad enough that it is embarrassing if it sits for a few hours.I bought the bike used with 19k on it.

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It shouldn't take 20 to 30 seconds to start. My bike has almost 35K and it starts in a couple seconds. When you said you tore it down for a color change, what did you mean? What you're describing does sound like rings. When cold, some oil can get by which the engine burns, and when it heats up the tolerances get tighter and the oil burning decreases or stops. I've also found that bikes with worn top ends that are slow to start like yours will fire right up when the top end is freshened. Maybe an over-oiled air filter? When you put it back together did you oil the filter? Did the hard starting begin after the bike was serviced or has it been like this? Have you run it much since the service? A drenched filter could account for this, but if you ran it enough it'd suck out the excess oil.

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The bike starts quickly and runs fine. It takes the bike 20-30 seconds to start smoking. I checked the air filter and if anything it is to dry. Sorry for the confusion. I changed the the color scheme from purple and white to silver frame with black plastic. I wish i would have known this was going to happen it would have been alot easier to work on when the engine was on the workbench.

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Mine with 18k also smokes like crazy when cold most of the time, but not always. Lasts for a few minutes. Enough that someone driving by might mistake it for a garage fire. I have a new piston and rings to put in some time when I get tired of making smoke.

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Mine did that as well with only 1800 miles, I tore it down for a bad crank bearing and the rings and seals were fine. Now I notice that its related to the use of the choke. If I start with no choke or flip it off immediately, it never smokes. Leave it on even partial choke and 20 seconds later its blowing clouds and takes a few minutes to clear up. Its white and smells more like oil than fuel but never does it if I restrict my choke usage to the minimum needed. In other word 1/2 choke to start only when its cold out then turn the choke off immediately and use throttle till warm.

This seems consistent with both the stock carb and FCR40!!

Bad rings smoke all the time, more so when hot. Bad intake seals can smoke on startup, but would then smoke more on decelleration when intake vacuum is high. Bad exhaust seals can smoke all the time if real bad, or on startup. Try modifying your choke behavior and see if it changes?

The last place to look is the breather vent to the air filter??

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Yes mine smokes more using the choke too. Half choke then off limits smoke here too.

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Stick your finger in the exhaust and see if it comes out oily. If not, it could be the choke like the others mentioned. If the exhaust pipe is oily then you know you're burning oil and a compression check would be a good idea. Another thought: since you had the motor out of the frame, check your cable routing. If it's binding or misrouted this could be part of the problem. Start the bike when it's cold and you're on the choke, then turn the bars from full left to full right and if the engine speed changes, then you know you have a cable catching on something. Maybe your problem is a simple as a cable reroute/adjustment. Good luck, and let us know how it turns out.

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I have a manual and took pics on disassembly of the cable routing. I have double checked them and I think they are right. I have the choke on the carb not on a cable. I will try the start without choke thing and see how it goes. I think that basicly that means on periods of high vacuum it is sucking oil from somewhere, rings seals etc. I hopefully already ruled out valve seals, that leaves rings as the main culprit. I think I will try a compression check tonight and see what it is. I have never done a leakdown check but if I have the equipment and time I may try that to. The PO did use synthetic oil and I changed to dino oil. I may switch back to see if that will buy me some time (money).

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I just did seals not guides and it showed no change at all in smoking. I was going to check compression but cannot find a 10mm sparkplug adapter.

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a compression test can be misleading. do a leak down test. you will be able to hear the air leaking from the crank case(bad rings) or carb(intake valves leaking) or exhaust(exhaust valves leaking). make sure your at tdc. 4-8% leak is okay, 10-12% is not so good.

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Some more random input to confuse things more.

These aren't real chokes, they are enrichners, so they won't increase engine vacuum. I agree that excess fuel should make black smoke not white, but for some reason excess enrichining (choking) on these DR's sure does make more white smoke??

Compression tests aren't too useful unless you take them regularly and look for changes. On a multi cyl. bike you can see one cylinder acting different, but on a single you really need a baseline reading from when it was healthy for comparison. Do it with engine hot and throttle wide open, then repeat after squirting oil in. If way better then your rings are suspect. Otherwise its hard to know what numbers are good for that particular bike and the test is worthless unless the throttle is wide open.

A leakdown test is way better, it tells you where the leak is and shows percent of leakage. Still best if you know a baseline reading for that bike when new.

Worn valve guides will allow the stem to pull the seal out of round and even new seals will leak. Synthetic oil will often prevent new rings from seating. That's a testimonial to its effectiveness. You have one chance to seat rings when the hone marks are fresh. Run synthetic when new and you can dull the hone pattern without wearing in the rings. This can screw up the break in process badly in some cases. After break in synthetic is good stuff.

With minimal choke I now get just a few seconds of whispy smoke,.. I can ignore that no problem. :thumbsup:

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Whats the thread pitch? 10 x 1.0?
Gut a plug and thread, weld or JB weld to it.

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I agree that excess fuel should make black smoke not white, but for some reason excess enrichining (choking) on these DR's sure does make more white smoke??

I think with a rich mixture on startup, there is a tendency to dilute or wash what oil was left on shutdown. Mix that with a cold piston/cyl that hasn't expanded and we have smoke. My 2¢.

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Well I just got the bike put back together and the smoke is gone. I ended up putting in new rings and piston. The reason I put the piston in is because after i got the cylinder off you could see where the PO had dinged the piston and then sanded the dings. It probably would have been OK but for under 60.00 for a new piston I didnt want to take it back apart. Now I have a intake leak to sort out but that shouldn't be to hard. It backfires thru the carb, I sprayed carb cleaner around intake boot and it dies. It's Easter and my wife wont let me work on it. If anybody has a easy way to fix the leak let me know. I think I can tighten the boot a little more, Ill just have to check.:p

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