Help with popping - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 16 (permalink) Old 01-09-2016, 10:41 AM Thread Starter
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Help with popping

Hi guys. So I went through the Verses and did most of the recommended checks/mods and procedures, spline lube, digital voltmeter, swapped the spark plugs for NGK iridium, etc.

I've done the coaster mod and I'm still getting lots of popping from the right hand pipe.

In the interest of full disclosure, here's what I've done:

Both mufflers were rotten off with no hope of welding or brazing so I got a pair of Sportster mufflers (with baffles intact) and de-goated. I don't have a cross over pipe because over here in Ireland we don't have too many dedicated exhaust shops and most of the ones that are here are fitters (I.e. Instead of fixing they just replace). I've had to wrap the headers solely because the right hand header pipe looked dreadful, chrome rust and no amount of polishing could help so I sanded off all the rust, used rust remedy to cure it and painted with vht paint (good to 800* C).

There is no leak from the connection of the muffler to the header, that's good, tight and sealed up.

I replaced the crush gaskets with the Harley Davidson ones, no leak from there.

As I said, I did the coaster mods and used the gaskets from the reed valves to seal up, they came of clean and I tightened up the bolts good and tight so there is no vacuum leak there. I have the air/fuel mixture screws turned out 2 1/4 turns on the left side and a full 3 turns on the right. The right carb vacuum hose is also sealed up well.

Leaves me with maybe 2 possible culprits:

I did pull all the hoses from the emissions system and didn't plug up the hole under the air box where I pulled the hose from.

I replaced the battery, I stupidly ordered the wrong Yuasa AGM battery online and it was costing me too much to return it so I just swapped it for a standard wet cell battery at my local bike shop. He had no AGM batteries in stock.

Could there be any other reasons why it's popping?

If it is one of the above reasons, why is it only popping from the right side exhaust?

Finally, will the popping damage my engine?

Sorry for the long winded post, I did try all the possible remedies I could find in the forums. I'm at my wits end and could really use your help.

Thanks guys.
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post #2 of 16 (permalink) Old 01-09-2016, 11:18 AM
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I'm thinking it may be running a tad lean, either due to the exhaust mods, a vacuum leak (leaky carb boot?), or dirty jet in the carb. Being on the one pipe indicates the condition exists in that one cylinder. Could check the spark plug for color to confirm. Opening up the exhaust most often requires larger jets in the carb.

These carbs also have a 'coast enricher'. If that malfunctions, the carb can be lean on deceleration.

The open hole in the airbox shouldn't cause the popping, but it's sucking in dirt.

The popping should cause no damage, since it's probably happening in the exhaust and isn't strong enough to hurt the exhaust system.

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post #3 of 16 (permalink) Old 01-09-2016, 11:40 AM Thread Starter
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Thanks a mill Spockster. I appreciate the reply, sounds like I might have to strip and clean the carbs to rule out those problems.

I have a couple of silly questions for you if you don't mind.

Can I visually inspect for a leaky carb boot without stripping the carbs out?

How can I tell if the enricher is malfunctioning?

I thought I only had to re-jet if I change the air intake, if I re-jet without having done an ear shave or changed my air intake at all, will it have any negative effect on the engine, carbs, plugs, etc?

Thanks again for the advice. It is very much appreciated.

Karl.
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post #4 of 16 (permalink) Old 01-09-2016, 12:04 PM
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You can check the boots for cracks or misalignment of the marks, but the best way is to spray around the clamp areas while running to see if the idle changes. Normally, a flammable spray is used, but propane or even water can work.

Not sure how to check the enrichers, other than visual inspection for cracked rubber, sticking springs, dirt etc.

In all my years of hot rods and wrenching, opening the exhaust a large amount has required jetting, and historically, that has been the practice for just about any gas engine. Simply changing air filters, has not. The whole rejet for air filters thing seems to have begun here and others have followed that. My bike is ear shaved with stock jets/stock pipes and does not run lean, others have tried the same setup with no problems.

I would not rejet unless my spark plugs show I need to. Assuming the carbs had clean jets to start with. When I earshaved, I asked here if rejetting was actually needed, I got no replies, so I decided to read my plugs first. I think most of these rejetted bikes are probably running rich.

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post #5 of 16 (permalink) Old 01-09-2016, 12:20 PM Thread Starter
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Thanks a mill Spockster. I'll run with your advice and let you know how I get on. It may take some time, my wife is giving me he'll for how much time I'm spending working on a bike that was meant to be "in great condition" and "needs very little done to it"!!!!!! Hahaha. Thanks again Spockster, I really do appreciate your help.
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post #6 of 16 (permalink) Old 01-21-2016, 01:53 PM Thread Starter
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Ok, so I sprayed some flammable loveliness on to the carb boots and the engine revved up...... Even revved when I sprayed on the rear cylinder carb boot the rear cylinder seems to be running fine. I can see that the tab on the front cylinder isn't lined up correctly, maybe a quater of an inch off, can't see the rear boot properly without stripping.
Could this be the cause?

Here are some pics of a plug pulled from the front cylinder.
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post #7 of 16 (permalink) Old 01-21-2016, 02:16 PM
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post #8 of 16 (permalink) Old 02-04-2016, 04:21 AM Thread Starter
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Ok, so here's where I stand...........
I did the Ear Shave and wanted to rejet to try and alleviate the popping, it turned out that the previous owner/workshop had refitted the rear carb boot on the front cylinder and visa versa........ I had my suspicions about this as the last job it did was to try and align the carb boot notches with the markers on the heads (which were horribly misaligned) and when I I'd, the carbs just sat totally wonky.......

Anyway, went at the ear shave....... Wanted to try run with 140/40 and no shims.......The pilot jets that the supplier sent me were keihin series 21 instead of 22...... Pain in the ass as they're not readily available here in Ireland so I'm gonna have to wait for a replacement pair........ I continued on anyway as I had already cut out the air box.......... Ran a hose from the crank case vent up under the tank to a K&n crank case filter. Running K&N pod filters too.

Sorted out the carbs boots, the carbs sat in lovely.

Put it all back together just fine and now there is no exhaust popping from the front cylinder (right side pipe where the problem was)......... BUT.......... Now my left pipe is popping worse than the right side was originally and instead of the bop, bop, bop of the exhaust....... It goes pfffft, pfffft, pfffft (there is pressure there when put my hand up to the muffler to feel the pfft, pfft, pfft).......there is also the odd pop from the front carb.

On a plus note, the right hand pipe sounds lovely...... Hahaha.

Is my problem the lack of shims and a need for a bigger pilot jets or could it be more sinister????

On a side note...... I ran the crank vent hose up under the tank and placed the filter in an aerosol cap to try and create that "dead air" scenario that I've read about, is this OK or detrimental???? It's not a snug fit, there is room for the filter to breathe.

Sorry for the long winded post...... Thanks again for any help.
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post #9 of 16 (permalink) Old 02-04-2016, 08:37 AM
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the crankcase vent does not require dead air, but it wont hurt any to be in dead air.. the carb vent hoses (2 hoses that join at a T fitting, then used to go to the right ear) MUST be in dead air.. those hoses lead directly to the top of the fuel bowls.. and air pressure fluctuations there will cause issues with the fuel level in the bowls.

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post #10 of 16 (permalink) Old 02-04-2016, 08:51 AM Thread Starter
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Thanks michiganteddybear, I have the carb vent hose hooked up to the nipple under the tank that covers the fuel level float jobby so should be good in that front........... Maybe...... Ha.
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