Carb tuning required for new exhaust?

I bought a running 1982 Maxim a month and a half ago, rode it 50 miles, and since then it's been apart as I slowly perform a safety upgrade: tires, brakes, and brake lines.

I've mentioned in a previous post that it has a 4-1 straight pipe exhaust with no baffles, and I absolutely can't keep that where I currently live. I bought a new Mac 4-1 system with baffles. My question is: when I put this new exhaust on, what are the chances that the bike will stop running well? I'm deathly afraid of having to rejet or something, more because I don't have the time than because I don't want to learn.

Like I said, the bike ran fine with the straight pipe. Maybe not absolutely perfectly tuned, but nothing obviously wrong. That said, it did pop quite regularly on deceleration so it may have been a little lean. My understanding is that going to a straight pipe can cause a lean condition, so adding baffles back in might make it run richer?

What do you think? Is this going to be a 1 hour swap or am I looking at a major job?

 

I think you'll be fine. From the sounds of it, the PO didn't re-jet for the straight exhaust. I would pull the plugs and see if your running lean.

http://www.mudinmyblood.net/forum/image ... _plugs.jpg

Generally speaking, if you switch from stock pipes to straight pipes you end up running too lean for the mixture screws to be of much help. Thus, the need to re-jet is necessary. However, if the PO put straight pipes on and didn't re-jet, odds are your new exhaust will be within the limit of the mixture screws.

I highly recommend you get a colortune. Makes dialing in those mixture screws a snap .One of the best tools I have ever purchased, second being the YICS eliminator. http://cgi.ebay.com/ebaymotors/YICS-Eli ... 0438814233

 

Mekon, I have a Mac 4-1 on my 650. Bike was tuned & did not need to rejet. You can see the story in m sig. It has been running (knock wood) problem free for over a year. The poping you mentioned is due to lean condition. After you have Mac installed if poping doen't go away you may need to tweek your mixture screws for the carbs slightly. Do some plug chops & check insulator color of plugs, your looking for a nice tan to chocolate brown color. As far as install time, depends on how hard the old system comes off, maybe 2 hours. Be careful removing the old exhaust nuts as the studs are prone to breaking & getting them out is a pita. Good luck & I think you will like the Mac.
Gregg

 

Yeah I'll bet anything the installer of the straight-thru system didn't rejet.

See how it runs afterward; you may need to tweak mixtures slightly but shouldn't have to re-jet if everything else (intake) is stock.

 

OK, thanks, it sounds like everyone is in agreement that it will probably only need minor tweaks. I'm hoping and praying that the PO didn't rejet... he didn't replace anything else, so probably not. The tires were 15 years old.

I wonder how long it's been running lean, and if it has caused any damage... bike has 33k miles on it, and is from Georgia... it was 94F today. I'll definitely take a look at the spark plugs when I swap the exhaust and post pics here since I don't know how to read them.

 

As long as he kept up on regular oil changes, running slightly lean shouldn't have done too much damage. Lean=HOT

Anxiously awaiting your plug pics

 

I'm sure he didn't... I sh*t you not, he sells me this bike that he *actively rides* and it has completely bald hard-as-a-rock tires and he says, "I haven't changed the oil in a little over a year so you should probably do that." And the air filter was solid black! 8O

*sigh*

Despite that, it does run strong and look pretty good. I think it has been garaged the whole time. Rubber lines are in good shape, minimal rust.

 

Well then, first thing I would do is drop a half a can of sea foam in the oil and start it up for about 30-45 seconds, then shut her off. Let it sit overnight. Next day, start her up again for about a minute. Then drain her, and give her some new oil and filter. Then clean the plugs up, set all 4 mixture screws to 2.5 turns out, and go for a 10 mile ride. Then re-check the plugs. Take pictures.

 

This is the first I've heard of seafoam in the oil, but I found a bunch of others recommending the same thing. Is that as controversial as seafoam in the gas tank? I was planning on doing an oil change, riding for 50 miles, then doing another one. Is the seafoam technique better?

 

New exhaust is on, sounds great, and the popping is gone. Crankshaft and final drive oil replaced, they were both filthy, and there were metal shavings on the magnetic drain plugs. I'm going to put a couple hundred miles on it then change the oil again.

Replaced the fuse box and the spark plugs today. Attached photo is the old plugs. Not a 'plug chop', this is from idle. No idea how many miles on these plugs. I don't know what the cylinder numbering scheme is, but these are in order as if you are sitting on the bike. I also don't know how to read plugs, but I think they look pretty good... charred or covered in oil at least.

 

"plug chop" should really be done on new plugs - that way you can actually assess the current running condition without being thrown off by the past. New plugs are nice in general too. Also, the insulators and base ring is what people want to see...not the outside threads. Take a picture (use the macro function) that looks down into the plugs.

Don't be afraid to rejet. Pain in the butt to be sure, but rejetting just means pulling the carbs out, taking 4 float bowls off, unscrewing an old jet out and screwing in the new one.

The exact size that will work for you is trial and error and a pain don't get me wrong, but it is nothing you should be "deathly" afraid of

 

Here they are from the front so you can see the first turn and insulators. This is reversed order from previous picture, so left-most plug in the photo is the right-most plug on the bike when sitting on it.

Gigantic versions of both photos in my gallery.

 

http://www.usaimports.co.uk/Mopar_Tech_ ... eading.htm

Here's some spark plug tech for ya,
You have pretty good coloration, #3 being a bit richer.