Top speed loss with Edelbrock?


16 replies to this topic
  • AdamW

Posted September 08, 2006 - 07:48 PM

#1

Since my new Edelbrock was installed, I have tried a couple full out top speed runs. I have yet to be able to get over 100 mph with 15/48 gearing. I am at 800 ft above sea level and run a #19 needle at 12 clicks out with a drilled airbox and stock air filter. It is not popping too badly at decel, just the put-put sputtering you expect from a fourstroke. No loud , isolated popping.

Why am I barely able to get to 100 mph with this gearing? I could almost reach it before with 14/48 gearing with the stock carb.

Any tips? Am I too lean?

Thanks,

Adam

  • snaggleXR650

Posted September 08, 2006 - 08:18 PM

#2

Lean on the top end no doubt. Edlebrocks are wonderful, but the design that makes them so easy to tune, also introduces tradeoffs. For example, to richen up one area causes lean spots in another. There was a big write up on this by Burned, the TT 'jetting expert' when he dyno tuned a DRZ with an Edlebrock and then a Keihin FCR. Regular carbs can be hard to tune, because there are so many fuel circuits, but this is what is required to dial an engine in at ALL throttle positions, at least until bikes come with fuel injection.

In summary, if you had a regular carb, I would tell you to go up a size or two on the main jet. With your Edlebrock all you can do is richen up your clicker and hope you don't suffer in the bottom or mid range. Good luck.

  • Old_Man_Time

Posted September 08, 2006 - 10:59 PM

#3

Since my new Edelbrock was installed, I have tried a couple full out top speed runs. I have yet to be able to get over 100 mph with 15/48 gearing. I am at 800 ft above sea level and run a #19 needle at 12 clicks out with a drilled airbox and stock air filter. It is not popping too badly at decel, just the put-put sputtering you expect from a fourstroke. No loud , isolated popping.

Why am I barely able to get to 100 mph with this gearing? I could almost reach it before with 14/48 gearing with the stock carb.

Any tips? Am I too lean?

Thanks,

Adam


I think Snaggle650 has a valid point. I noticed that the Edelbrock did not have the brute force pull that my stock carb seemed capable of when the throttle was rolled on completely. Many felt I was nuts or my Edelbrock was not tuned properly. I still stand by that seat of the pants feeling.

Having said that let me very clearly state I would not go back to stock unless you pried my Edelbrock from my cold dead hands. It is so smooth and runs consistently better than stock in every other way except top speed.

I personally feel that the benefits of the Edelbrock compared to the stock carb out weigh any losses in top end speed. The fact that you are popping a bit on compression slow downs seems to be a lean condition. You may be able to get a bit more top speed simply richening the circuit a couple clicks.

I have read that the other two pumper carbs which both have jets are capable of higher performance gains than the Edelbrock. I also have read to get them spot on is very difficult but well worth it once achieved. I'm lazy so the Edelbrock serves me well.

  • snaggleXR650

Posted September 09, 2006 - 06:22 AM

#4

I think that's the ticket. I use a Mikuni TM-40 and I have spent weeks worth of time here and there dialing it in for different mods on my bike. It is a PAIN to tune by the seat of the pants, but once it's setup properly... Fortunately, the carb can be rotated on the bike and rejetted without fully removing the carb from the boots, otherwise, I would have thrown the carb over a bridge along time ago :thumbsup:

I'm not knocking the Edlebrock, If I had to buy another carb right now I would give it a shot. It's got some wonderful features, and I'll be honest in that I don't really understand how it works, but from what I do understand you have a needle and click positions. This is basically 1.5 circuits compared to my Mikuni's 5.5 circuits (I'm counting raising/lowering the needle as a half circuit). Maybe there is a way to dial in an Edlebrock at ALL throttle positions, but it's unlikely without having some lean and rich spots.

  • InternalCombustion

Posted September 09, 2006 - 07:49 PM

#5

The QS manual states that the Metering Adjustment Tool (MAT) is used to make adjustments to the mixture, but only from idle to mid-range. Any adjustments needed above mid-range (such as your issue on top-end) would be made by changing your needle size. Your kit should have shipped with two extra needles, a #17 (smaller/leaner) and a #21 (larger/richer).

Back to basics:

1. Did you correctly spec you QS when you ordered it? You did not say where you sourced your new QS from. If you got it from Barnum's they normally have it dialed in for your bike's equipment.

2. You are running 15/48, but is that with the factory 18" rear rim? (I am also running 15/48 but with 17" SM rims and tires. I hit the factory rev limiter at about 95 mph (but 95 comes real fast). I have a set of 16/44 sprockets on a UPS truck headed this way. So, are you running the 18" rim?

3. You say your airbox is drilled and you are running a stock filter. What about pipe? I assume you've either got an HRC tip on your stock pipe or you've got an aftermarket pipe. If you're running with either of those exhaust options, AND you got a correctly spec'd QS, you should be seeing in the neighborhood of 103-104 with your 15/48, no prob. So, what about your pipe?

4. So... I think you are going to find you are running rich, which if you are running the #19 needle, means you've got an airflow restriction somewhere in the intake or exhaust. (Even though you say your getting some mild popping on full throttle closed decell, a #19 needle at 12 clicks out sounds to me to be too rich at idle-to-midrange.) I may be waaay off here but I would expect you would have your MAT set at maybe 18-19 clicks out. BWB63 is running a bad-boy 680, built to hell and back and he's only running 16 clicks out, with a #19 needle. But, in any case your MAT setting should not be impacting full-throttle top speed.

5. If you don't get any other suggestions try this: during a high-speed run, when you are maxed on your speed, roll the throttle off just a bit. If you feel a surge of power then you are running rich. If you do NOT get a slight surge you are either spot on or running lean.

Check for rich mixture, and give us some more info on your setup. I hope I haven't confused the issue here.

Ride safe on those high-speed tests! :thumbsup:

  • HawkGT

Posted September 09, 2006 - 08:00 PM

#6

...during a high-speed run, when you are maxed on your speed, roll the throttle off just a bit. If you feel a surge of power then you are running rich...


Other way around. A momentary surge in power means you're too lean.

ETA: Umm--wait, I could be wrong there. The Edlebrock may work opposite a "normal" slide valve carb with respect to that roll-off test. If that's the case then ignore me....

  • Mudshark

Posted September 10, 2006 - 09:54 AM

#7

Other way around. A momentary surge in power means you're too lean.

ETA: Umm--wait, I could be wrong there. The Edlebrock may work opposite a "normal" slide valve carb with respect to that roll-off test. If that's the case then ignore me....


Is this is what you are referring to HG?
Taken from the Mikuni web site:
"ROLL-OFF:

The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.
If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.
If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one."

  • InternalCombustion

Posted September 10, 2006 - 12:23 PM

#8

Other way around. A momentary surge in power means you're too lean.

ETA: Umm--wait, I could be wrong there. The Edlebrock may work opposite a "normal" slide valve carb with respect to that roll-off test. If that's the case then ignore me....

I had to think about this a while this morning, because Johnnie Walker was helping me type last night... So, when all else fails, open the manual. :-)

Yeah, you and MudShark are correct, for the Mikuni and many other carb designs. But the QS reacts opposite to the rolloff test, than the Mikuni. Again, the manual states that a rich condition is indicated if the bike "...accelerates when wide open throttle is rolled closed slightly.". Confusing, but there it is, p.5.

Anyway, I think the key point in this thread right now is we need more data on the bike's current config. Everything suggests to me a rich state. A QS MAT dialed only 12 clicks out on a #19 needle seems too rich for a standard "uncorked" (fully uncorked??), stock-cam 650R.

And a #19 needle should be plenty big for all but really extreme 650R mods. So, if he's not producing expected power and he's not running lean (#19 needle...), he's running rich. Which in turn means a stock, "corked" pipe or clogged or otherwise restrictive air filter.

Another point to check would be his spark plug condition. It may be that if I am correct (???) on 12 clicks out being too rich (idle-to-mid-range) the plug may be fouled.

We need more data.

Ride safe.

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  • Mudshark

Posted September 10, 2006 - 12:49 PM

#9

Johnnie Walker was helping me type last night... .

Aha! red, black or blue??

I think the key point in this thread right now is we need more data on the bike's current config.
Another point to check would be his spark plug condition. It may be that if I am correct (???) on 12 clicks out being too rich (idle-to-mid-range) the plug may be fouled.
We need more data.

too true. :thumbsup:

  • InternalCombustion

Posted September 10, 2006 - 01:27 PM

#10

Aha! red, black or blue??

Red. I put too much money into the BRP to afford Black or Blue... :-)

  • Old_Man_Time

Posted September 10, 2006 - 01:33 PM

#11

You guys are right. I have a Hotcam stage one with my Edelbrock with a #19 needle and between 17 to 19 clicks to run perfectly. I never paid much attention to the fact that he said 12 clicks. That is too rich not lean. I am glad some of you are much more careful readers than I was. :thumbsup:

  • HawkGT

Posted September 10, 2006 - 01:58 PM

#12

Yep, we're all on the same page on the roll-off test. At first I was thinking--no that's wrong, it works the other way around. But then I thought--uhh, the Edelbrock is an air-metering carb similar to a Lectron so it may be just the opposite what we're use too with traditional fuel-metering carbs.

Carry on... :thumbsup:

  • Mudshark

Posted September 10, 2006 - 07:14 PM

#13

Red. I put too much money into the BRP to afford Black or Blue... :-)


hehe.. me too... my excuse is that I ride a Red bike now so I have to choose red label... :thumbsup:

  • AdamW

Posted September 12, 2006 - 03:43 PM

#14

Thank you to all for your replies.
My bike has a stage 1 hotcam, stock exhaust with HRC tip, stock wheels, 15/48 gearing.

I chose to richen the MAT to 12 clicks because it felt noticeably sluggish with WOT applications before I did this. The kind of BWUUAAAAAHH you get from a tired two stroke with a peaky powerband. The richer setting solved most of this.

I should note and this may be an importand factor, I am at exactly 800ft above sea level and it has been a little cooler here lately.

Hope this helps. I will try all suggestions. I am not a speed freak by the way. I just want to know that my carb setting is optimum.

Thanks again to all.

Adam

  • InternalCombustion

Posted September 12, 2006 - 06:35 PM

#15

Thank you to all for your replies.
My bike has a stage 1 hotcam, stock exhaust with HRC tip, stock wheels, 15/48 gearing.

I chose to richen the MAT to 12 clicks because it felt noticeably sluggish with WOT applications before I did this. The kind of BWUUAAAAAHH you get from a tired two stroke with a peaky powerband. The richer setting solved most of this.

I should note and this may be an importand factor, I am at exactly 800ft above sea level and it has been a little cooler here lately.

Hope this helps. I will try all suggestions. I am not a speed freak by the way. I just want to know that my carb setting is optimum.

Thanks again to all.

Adam

This is a tough one

Just to be sure on all points (I'm not trying to be clever or an ass, just trying to make sense out of your problem):
- you know for a fact the needle in your QS is the #19, right?
- when you say 12 clicks, you are referring to 12 clicks OUT (from full clockwise IN)?
- thanks for the altitude and temp data. 800' and cool temps shouldn't be effecting you. I am at about 1000', running a T4 system, stock cam, Uni, vented side cover, a #19 needle, 18 clicks out on the MAT, 15t/48t gearing on 17" rims and I can hit the rev limiter, hard, in 5th.
- I know you said cranking in the MAT seemed to smoth out the problem a bit, but the manual clearly states the MAT does not impact mid-to-full power mixture, only idle to mid-power.

Wildcard question: do you feel like the bike is producing a proper power curve at lower revs, but the power curve simply flattens out at higher revs? Or is it sluggish through out the rpm range?

Three suggestions, in increasing order of pain:

1. Check your plug for a proper medium-tan color (per earlier post).
2. Check your air filter is clean, and not over-oiled
3. Do a roll-off test (per earlier post)
4. Go into the QS and spec the needle, float / fuel shut-off valve, etc.

Let us know on 1-3, first.

  • creeky

Posted September 17, 2006 - 06:47 PM

#16

If you suspect it is running lean on top, why not try a 20E needle??

  • Pbar

Posted January 19, 2007 - 09:47 PM

#17

Nothing beats the old fashion method of the spark plug check.





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