Possible problem with QS carb.

13 replies to this topic
  • JackAttack

Posted January 13, 2004 - 10:02 PM


I installed an Edelbrock QS carb about 800 miles ago. I was not sure what angle to install it, so I made it so the bottom of the bowl was level when the bike was off the kick stand and standing straight.

I recently purchased a Clark 4.3 tank, excellent quality I might add. When removing the stock tank I noticed that it had a small wear mark in the plastic where the corner of the top of the carb had almost worn a hole thru the tank. It had come very, very close to making a hole in the tank near the exhaust header.

This possible hole in the tank would never have been visible without me taking the tank off. All it took was a simple twist of the carb to relieve some of the pressure that it was creating on the tank.

Just a heads-up to those using the stock tank with the QS. It is possible that it could create a fuel leak if installed so that it comes in contact with the tank. The Clark tank however has plenty of room so that the carb does not come in contact with the tank.

Ride on! :)

  • irondude

Posted January 13, 2004 - 10:41 PM


Seems like the fix is just to mount the carb at a slight angle. I have used the Edelbrock with the stock tank, the IMS 3.2, the IMS 4.6 and the Acerbis 6 gallon tanks all without any rubbing. Over 10K miles on the mighty Edelbrock, without any fit issues.
But there is a related phenomenon here: Aftermarket parts that rub against other aftermarket parts. i.e. the aftermarket part may work fine replacing a OEM part, even if the new part is bigger or smaller or just slightly a different shape. BUT all to often aftermarket parts DONT fit right when they are near other aftermarket parts.
For example my Ohlins rear shock resevoir rubs against my IMS tanks. My new IMS radiators WONT take the Devol radiator guards, etc. I guess theres no way around it, as the aftermarket guys obviously cant measure their part with every other aftermarket part....

  • qadsan

Posted January 13, 2004 - 11:01 PM


My Edelbrock QS had plenty of room underneath my Clarke 4.3. I have a stock tank, an IMS 3.2 and the Clarke 4.3, all with different graphics on them along with different seats & shourds with different graphics. When I get bored with the look, I simply switch out the seat, tank & shrouds and I've got a diferent looking bike :) In anycase, I was removing and re-installing the tanks and never noticed any rubbing issues with my QS carb on any of the tanks and that's something I specifically look for, but then my QS carb is the older style with the billet bowl and perhaps they've changed or perhaps the Clarke tanks have changed or??? One thing that's interesting is that the Clarke tanks used to fit on the California bikes without issue, then a ways back people started having problems with the Clarke's not fitting unless the PAIRs smog stuff was removed. Maybe both products have changed enough to cause this potential interference over the last year or two?

On a similar note, when a few dozen XR650R riders including myself bought QS carbs together back in 2001, two of the guys had fitment problems when their carbs came in contact with the Bomb portion of their FMF PowerBomb header. One guy chose to indent his header as a fix and the other guy chose to run his carb slightly canted. I recall Rob Barnum saying that running the carb at a slight angle is no problem at all in terms of how well the carb will perfom.

That's a very good point about the carb hitting the tank and people should check that out more closely incase there's a problem, but as irondude pointed out, there are no rules as to how aftermarket parts are supposed to fit together with other aftermarket parts, but it would be nice if both Clarke and Edelbrock made a note in their installation instructions to check for possible interference if they don't already do so.

  • cat0020

Posted January 14, 2004 - 07:58 AM


I've got a set of Acerbis front and rear tank with the Acerbis saddle that specifically fit the rear tank.
I am wondering if the installation of these items are difficult. Currently my XR has the stock tank with Quicksliver carb. I don't notice any rubbing against the stock tank.

  • nickn

Posted January 15, 2004 - 12:45 AM


After 12 months on the bike I had the same problem. I was kicking myself that I didnt think to check, very easily done.

  • irondude

Posted January 15, 2004 - 09:17 AM


I've got a set of Acerbis front and rear tank with the Acerbis saddle that specifically fit the rear tank.
I am wondering if the installation of these items are difficult.
I have the front and rear Acerbis tanks also- i run them with the Edelbrock with NO PROBLEM.

However-there are fit issues with the rear tank/seat. I had to re-drill the holes for the rear tank bracket to line up with the sub-frame. Also-trying to remove the air filter cover with that tank on is a [@#$%&!]. Finally i had to put a fuel filter between the two tanks, as dirt was getting into the rear tank.
OH Yeah- 3 times now i have brocken the plastic filler cap on the rear tank with my boot while getting off the bike. I need to find an aluminum rear cap.
The bike is about 1.5 inches taller with that rear tank/seat. Interestingly-the rear seat/tank will work with the 4.6 gallon IMS tank. Its 35 miles less range, but a much more ridable set up. That Acerbis front tank is WIDE.
Perhpas the best set up would be the 7 gallon IMS tank in front, and the Acerbis tank/seat in the rear with the Edelbrock adjusted slightly lean. I havent tried it yet (not sure anyone has) - so not sure about fitment. BUT--This should give well over 300 mile range with the CG much lower than the full ACERBIS set up....add in a lowering link, and thats a serious set-up! More than enough for round the worlding, Dakar racing, or just back country exploration.
Throw in some quick detach additions to the fuel lines, and get a brass 'T' for the two fuel tanks....the plastic unit from Acerbis is weak.
Lets see a picture of your BRP with 10 gallons of fuel!

  • jaybert600

Posted January 16, 2004 - 08:13 AM


I have removed the stock tank last night and also noticed wear. I removed the part of the carb that was causing the problem and ground it down to clear the tank. Any idea how thick the plastic is in that location? Also, it would not work for me to rotate the carb because the bowl comes so close to the header.

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  • qadsan

Posted January 16, 2004 - 09:21 AM


This topic is getting more interesting. Where abouts does your carb hit? Is it a bracket on the carb that's hitting the plastic or the carb body itself that's hitting the plastic? Where exactly are the carbs hitting the tank? On the front left, rear top right, etc? Are these all newer style carbs with the cast style float bowls or the billet bowls? Just curious...

  • jaybert600

Posted January 16, 2004 - 09:45 AM


It's the top right-hand corner of the carb. It is the corner of a "C" shaped plate that holds the top of the carb on. The only way to see it is to look up and forward with a flashlight underneath the tank (it may be already rubbing and you may not notice it until tank removal because of obstructed view). Basically, anyone with a QS should check this out and Edelbrock should be notified. My carb has a billet bowl, so I don't know of any differences with newer versions. I removed the plate and rounded the corner with a bench grinder to make it clear.

  • irondude

Posted January 16, 2004 - 11:30 AM


You might want to talk to the guy who designed the QS for the XR650--Rob Barnum. He is also the largest distributor ot QS carbs for our bike. He is also a passionate XR650 racer--so if anyone has the answer--it'll be him. There are hundreds of QS carbs on 650's with stock tanks. Obviously you have a legitimate concern. But some perspective here: I have raced my 650 through the Laughlin Hare Scrambles--arguably the toughest desert race, without any rubbing between the stock tank and the Edelbrock. SO its NOT a design issue found on ALL QS carbs... If it where-we ALL would have the problem. We dont.
Dont mean to de-legitimize your problem-you have a real problem!!--just stating that mine doesnt rub with stock or aftermarket tanks...my suggestion would be to contact Rob.

Maybe yours has incorrect parts, maybe your bike didnt come with a rubber mat over the frame (or it slipped down, or worn out), maybe you have other after market stuff, maybe you have the wrong carb, maybe you dont have the rear of the tank properly secured, maybe your carb is from a KTM. Maybe the carb is to far into or out-of the manifold/and or boot. Maybe the cables are pinched.
I have heard of all of these scenarios, and for sure there are many other reasons. Just tryin to be helpful...


  • JackAttack

Posted January 16, 2004 - 11:56 AM


I don't think that it is a very large concern, just something that should be checked on. The problem should be remedied with a few adjustments(twist carb or shim tank). I believe it is impossible to see it rubbing when the tank is on the bike due to the location of the rubbing. I don't have time to further investigate it out right now. I will be riding in Mexico this weekend and will be putting the stock tank back on next week. I should have more to add then. :D

Irondude(both of you :)),
The first thing I thought of was the rubber mat possibly slipping out of place between the tank and the frame, I will check that first. I think your right about it being something just a little out of spec. I don't believe there is any problems with the carb itself, it kicks ass.

  • JackAttack

Posted January 23, 2004 - 12:22 PM


I put my stock tank back on my bike yesterday.

Jaybert600, that is exactly the problem. The square edge of the bracket is the part that digs into the tank. I used a die grinder to round off the corner, took quite a bit off. I did'nt have to move the carb at all. I'm glad I caught it in time. I think it would have worked its way through the tank in a few more rides.

I got my carb through White Bros., I assume they are all the same. Maybe Barnum fixes the problem before he sends his carbs out. :)

Ride On :D

  • jaybert600

Posted January 25, 2004 - 06:50 PM


The groove in my tank was deep enough (in my mind) to warrant a replacement tank. I bought another stocker on Ebay and installed it this weekend. It's not close to the carb at all! There must be a pretty dramatic production tolerance in plastic gas tanks! Also, I spoke with Edelbrock about this last week. They said they have never heard of this problem, but would "look into it." In my opinion, everyone with a QS should check the clearance between the carb and tank (viewable by removing the tank or looking up underneath the tank at the upper RH side of the carb) regardless of which tank they have.

  • qadsan

Posted January 26, 2004 - 08:17 PM


I bought another stocker on Ebay and installed it this weekend. It's not close to the carb at all! There must be a pretty dramatic production tolerance in plastic gas tanks!

Very Interesting info and this has been a good thread to learn from :)

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