Donvito Posted July 27, 2013 Share #1 Posted July 27, 2013 My 87 VR backfires when coasting. Sounds more like a chirp, not too annoying but would like to stop it if possible. Seems to be coming from the left side. I tried running with the choke slightly engaged and that stopped it. So, I am thinking that I should turn out the idle screws to idle richer. How many turns out would be the maximum? Or, it's the coasting enrichment valve in which case I'll probably live with it until I do the carbs again. Any suggestions? Link to comment Share on other sites More sharing options...
Huggy Posted July 27, 2013 Share #2 Posted July 27, 2013 (edited) How do your plugs look? I'd check the plug color before I start turning things. and you probably need to do a carb sync!!! Edited July 27, 2013 by Huggy Link to comment Share on other sites More sharing options...
Venturous Randy Posted July 27, 2013 Share #3 Posted July 27, 2013 Most likely an exhaust leak pulling in oxygen during coasting and refireing. RandyA Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #4 Posted July 27, 2013 Most likely an exhaust leak pulling in oxygen during coasting and refireing. RandyA That's what I thought originally but that doesn't explain why it stops when the choke is engaged. Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #5 Posted July 27, 2013 How do your plugs look? I'd check the plug color before I start turning things. and you probably need to do a carb sync!!! Just changed the plugs and the ones I removed were a light grey color. Just synced the carbs also. Just did the valves last week also. The backfire has been happening for a while just can't seem to get it to stop. As I said, it doesn't backfire when the choke is partially engaged so that's why I thought it may be a lean mixture igniting in the exhaust. Link to comment Share on other sites More sharing options...
Huggy Posted July 27, 2013 Share #6 Posted July 27, 2013 (edited) I'm going to check with some one who knows a little more but I still think a carb sync is in order. what RPM are you idling at? I would just turn out enough to see if it stops and only make the adjustment after the engine is warmed up. Go for a ride then adjust. Idle speed 1000 RPM max. Low side 950 RPM. Edited July 27, 2013 by Huggy Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #7 Posted July 27, 2013 I'm going to check with some one who knows a little more but I still think a carb sync is in order. what RPM are you idling at? I would just turn out enough to see if it stops and only make the adjustment after the engine is warmed up. Go for a ride then adjust. Idle speed 1000 RPM max. Low side 950 RPM. It idles dead on 1000. Synced the carbs after I changed the plugs this morning. Installed E3 plugs but it was back firing before with the NGK's. Link to comment Share on other sites More sharing options...
Huggy Posted July 27, 2013 Share #8 Posted July 27, 2013 Is it still backfiring with the E3's? Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #9 Posted July 27, 2013 Is it still backfiring with the E3's? Yeah. Sorry for the confusing post. It was backfiring with the NGK's and it's still backfiring with the E3's. Link to comment Share on other sites More sharing options...
Huggy Posted July 27, 2013 Share #10 Posted July 27, 2013 Yeah. Sorry for the confusing post. It was backfiring with the NGK's and it's still backfiring with the E3's. Now that I think of it it could be that because it is coasting you are dumping unburned fuel into the cylinder(s) and that's why it is popping/back firing. In that case you cannot do much about it. Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #11 Posted July 27, 2013 I recall reading a post a while back where someone said it could be from a too rich or too lean condition as well as other causes such as exhaust leaks. I thought I had eliminated the "too rich" possibility because it stopped when I enriched the mixture via the choke. So, I assume it's the "coasting enrichment circuit" but I thought I may be able to compensate by enriching the idle mixture for now until I do the carbs again. I have isolated the problem to number 2 cylinder and I improved the backfiring by backing off on the idle adjustment screw but it is now at 5 1/2 turns and the backfiring is just about gone. I'm just not sure if that is too high an amount of turns and if it is OK to leave it at that setting? Link to comment Share on other sites More sharing options...
dysfunctional33 Posted July 27, 2013 Share #12 Posted July 27, 2013 5 1/2 turns is way too much. 3 1/2 is usually the max you want to be turned out. At 5 1/2. You are making a very rich condition. You may need to replace your main jet or at least clean it. Check and make sure the carbs are seated all the way in the boots on the bottom also. Link to comment Share on other sites More sharing options...
Donvito Posted July 27, 2013 Author Share #13 Posted July 27, 2013 5 1/2 turns is way too much. 3 1/2 is usually the max you want to be turned out. At 5 1/2. You are making a very rich condition. You may need to replace your main jet or at least clean it. Check and make sure the carbs are seated all the way in the boots on the bottom also. I know I read you can check for vacuum leaks by spraying something and seeing if the rpm's increase but I don't remember what to spray. Link to comment Share on other sites More sharing options...
dysfunctional33 Posted July 27, 2013 Share #14 Posted July 27, 2013 WD40 works. I used starting fluid when I checked mine cause I already had it laying around. I've also seen some people use a propane torch, not sure how well that works though Link to comment Share on other sites More sharing options...
Huggy Posted July 28, 2013 Share #15 Posted July 28, 2013 Check the vacuum tubes for leaks also. But usually if you have a vacuum leak it is very hard to get a good carb sync. Link to comment Share on other sites More sharing options...
Venturous Randy Posted July 28, 2013 Share #16 Posted July 28, 2013 I I have isolated the problem to number 2 cylinder and I improved the backfiring by backing off on the idle adjustment screw but it is now at 5 1/2 turns and the backfiring is just about gone. I'm just not sure if that is too high an amount of turns and if it is OK to leave it at that setting? If you messed with the idle adjustment screw that much, there is no way the carbs are in sync. Did you mean the air/fuel mixture screws? RandyA Link to comment Share on other sites More sharing options...
dysfunctional33 Posted July 28, 2013 Share #17 Posted July 28, 2013 Check the vacuum tubes for leaks also. But usually if you have a vacuum leak it is very hard to get a good carb sync. I was able to get a good carb sync 3 times with a pretty good vacuum leak. It took me awhile to figure out what was wrong because I thought the same thing Link to comment Share on other sites More sharing options...
GeorgeS Posted July 28, 2013 Share #18 Posted July 28, 2013 IF , you end up pulling the exhaust system, to sort this out, best to order a complete new set of Gaskets ( ie: seals ) for the entire exhaust system. Most likley some of them will have to be replaced, might as well do them all !! Not cheap, but money well spent !! Link to comment Share on other sites More sharing options...
Donvito Posted July 28, 2013 Author Share #19 Posted July 28, 2013 If you messed with the idle adjustment screw that much, there is no way the carbs are in sync. Did you mean the air/fuel mixture screws? RandyA Yes, I meant the air/fuel mixture screw. The idle adjustment screw is set at 1000. Link to comment Share on other sites More sharing options...
Donvito Posted July 28, 2013 Author Share #20 Posted July 28, 2013 Check the vacuum tubes for leaks also. But usually if you have a vacuum leak it is very hard to get a good carb sync. What's the best method to check for leaks in the vacuum tubes? I'm aware of the vacuum tube attached to the vacuum port under #2 carb, are there others and where are they? Link to comment Share on other sites More sharing options...
Huggy Posted July 28, 2013 Share #21 Posted July 28, 2013 What's the best method to check for leaks in the vacuum tubes? I'm aware of the vacuum tube attached to the vacuum port under #2 carb, are there others and where are they? I should have said the vacuum tube caps. I had that problem on my XJ. The caps looked good and felt good but the where leaking. And using propane or what ever does not ALWAYS show where a vacuum leak is. It did not show that MY vacuum caps where leaking! Link to comment Share on other sites More sharing options...
Donvito Posted July 28, 2013 Author Share #22 Posted July 28, 2013 (edited) I have been trying to eliminate a backfire chirp for the past several months. Originally, it would do it at idle but, now, it only happens when I decelerate and coast. If I slightly engage the choke, it stops, so, this led me to believe I am dealing with a too lean condition in one of the cylinders causing the unburned fuel to ignite in the exhaust pipe. I was able to isolate the problem to #2 cylinder and eliminated the backfire by adjusting the air/fuel mixture screw. It decreased as I backed out the screw and stopped at 5 1/2 turns. I have done a lot of maintenance over the past couple of months and these are the items related to the engine: changed to E3 spark plugs adjusted the valves synced the carbs tried to order diaphragms but they are out of stock so did the Plasti Dip treatment did the Sea Foam treatment searched for vacuum leaks using WD 40 So, at this point, I believe the problem is either in the "coasting enrichment valve assembly" or a vacuum leak. To get to the "coasting enrichment assembly" I have to pull the carbs and the bike is running too good at this time to do that. So, if it is a vacuum leak somewhere, how do I find it? I know #2 carb has a vacuum hose running from the vacuum port below the carb to a plastic enclosure but I don't see any problems with it. Is there a way to test it or should I just replace it if available. What harm am I doing by running with #2 carb at 5 1/2 turns out other than decreased gas mileage? Should I leave it like that or live with the backfire? I am attaching pictures of #2 carb including the spark plug after a ride and letting it idle for about 5 minutes. Edited July 28, 2013 by Donvito Link to comment Share on other sites More sharing options...
Huggy Posted July 28, 2013 Share #23 Posted July 28, 2013 I don't think that plug should be that clean if you turned the screw out that far!! I would think it would be black from being to rich of a fuel mixture. Link to comment Share on other sites More sharing options...
Donvito Posted July 28, 2013 Author Share #24 Posted July 28, 2013 I don't think that plug should be that clean if you turned the screw out that far!! I would think it would be black from being to rich of a fuel mixture. You got me thinking so I put it back together and ran it to confirm that #2 cylinder is running. It is. That is the way the plug came out of the bike. I didn't clean it. Link to comment Share on other sites More sharing options...
dysfunctional33 Posted July 28, 2013 Share #25 Posted July 28, 2013 Was that plug wet when you took it out? Have you tried taking the air filter out and looking down through the air box to see if all of your slides are moving freely. If you know the problem is #2 I'd say you have a bigger problem than just a vacuum leak Link to comment Share on other sites More sharing options...
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