As some of you know, we screwed up some stuff on my bike. After making the adjustments we made (about a week or two ago), the bike started back firing out of the exhaust pretty bad when you let off the throttle. I also started experiencing a flat spot in the mid-range of my throttle. I took the bike in and had it dyno tuned. It's still backfiring out of the exhaust when you let off the throttle and I still have that very significant flat spot in the mid-range of my throttle so I called the mechanic up and talked to him. This is what he told me.

Can the following statement actually be true???

"Both of those issues can be attributed to the bike being tuned properly."

According to the mechanic, even though I did not have that flat spot in my throttle before we screwed it up...and even though it wasn't back firing...and even though it was pulling a LOT harder than it is now after being dyno tuned, it can all be blamed on my exhaust and the fact that it wasn't dialed in perfectly. This doesn't make logical sense to me. Can that be an accurate statement???

I'm trying to figure out if I can trust this shop. So far, my experience with this particular mechanic at this shop has not been the best...and I think he's blowing smoke up my *** to try to cover his. The only problem is, I don't really know enough to call him out.

I'm trying to learn how to wrench on my own ride. That's obviously going to take a while. In the mean time, would you trust anyone that tried to tell you what this guy told me? He also told me to take a rag and plug up the left side of my exhaust, go for a short ride to see if it's still backfiring. I cannot get a rag to stay in the exhaust, no matter how tightly I shove it in there.

 

He is full of ****, nobody sticks a rag up their exhaust and expects it to stay there.....

So if he can tell you that then he is not worth bothering with.

What pipes, air cleaner and carby do you run?

Backfiring down the pipe is usually a lean condition caused by wrong jets or mixture adjustment, an airleak or baffled pipes...all of which could cause a flat spot (especially with drag pipes).

 

put me in coach i also agree -

did the guy with this dyno give you a sheet - with a graph hopefully showing the AF and the power the bike made and what it was before he adjusted it then after would be a nice add for your money

 

I am no mechanic but neither is any idiot that tells you to put a rag up your exhaust!!!!

 

The shop that dyno tuned it told me that I had stock headers. I know I have Hooker pipes. I have a Mikuni HSR 42/45 carb with what appears to be some kind of K&N air filter. I don't know if it's a high flow air filter or not. It fits under a 88" air cleaner cover and trim plate and up against one of those 3 bolt plates (that I assume is standard with the Mikuni carb kits).

The mechanic that dyno'ed it said the bike is actually running a little rich but not enough to mess with the jet...so I think I can rule out the running too lean as a potential problem. He advanced my timing by 4 degrees and we had played with the timing advance trimpot on the Crane Hi-4. I don't know if the timing might be the culprit on the backfiring or not... If it's an air leak, it coincidentally started the exact same day we screwed with my adjustments. I appreciate the feedback!

 

Yes, but like I said, it was running FAR better a week before we screwed with the adjustments than it is now after we messed it up and subsequently took it in to have it dyno tuned. According to the dyno graph, it ran IDENTICALLY when I took it in as it does now after being dyno tuned up until you hit 72 mph. After that, he gained me about 3 hp (at about 110 mph) by advancing my timing 4 degrees and adjusting my carb. He timed it with the dyno...and did not use a timing light. Keep in mind that I did NOT have this flat spot, or the back firing before we screwed with my adjustments. It was also pulling a LOT harder. Thank you for your feedback!

 

lol...

 

Then you have to rub a lamp and ask the Genie why you can't put your bike back to the good settings and have it run like it used to???

I believe you have tried to do that and it didn't work which suggests two things to me:

1: You can't find your original settings

2: A fault has developed since or during that bout of tuning that caused the problem.

If you explained in detail what you did then it might throw up a clue....there is also a formula.....man works on bike, bike doesn't run properly = go back and look hard at the last thing you did.

It is easy to go back over what you did and assume that one thing is OK when in fact it isn't because something else you did affected it but you didn't join the dots....not saying you are thick or anything, just trying to pass on some wisdom I picked up from similar scenarios.

Then again, sometimes you have to walk away and come back later and look at the problem without referring to the work you did before....this is why some shops can fix a bike when the owner cannot, because they take things at face value and fix the fault they see, not the issue you think you have.....hope that helps!

 

Dyno tuning is a waste of money. (flame away)

If a bike is running well why bother with tuning it!

How often do you run 80 to 100 mph??

Why tune for the top end when most(maybe all) of your time is spent below 3500RPM.

Buy a crotch rocket to go racing, they are made for it and are throw-away bikes. A Harley isn't. They are mostly built for long/short distance cruising. Drinking beer and chasing skirts.

By tuning up to maybe past the rev limiter there is no telling what happened internally to that engine, flywheels, cam timing, bent pushrods, breather timing, any number of things can and will cause your problems.

There are several people on here that can and will help you out, I'm not one of them because I keep all my bikes stock, but you are in the right forum.

Good luck!

 

I'll add my .02 on the dyno tuning... Unless you have an O2 sensor , the ONLY way you're going know if that bike is where it needs to be air/fuel ratio, is on a dyno. Yes, there are some guys that can get it near where it needs to be by ear and riding it believe it or not, but if you have a built motor, It should be tuned unless you are real good at tuning.! lean that puppy out on the top end or hell, even cruising it on hot day and get on it and it's lean, BOOM!