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Bigger cams runs richer

  • Thread starter Thread starter gearhead13
  • Start date Start date
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gearhead13

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I installed a set of bigger cams, about 15 deg more duration and more lift. The bike runs too rich now:confused: Seems the opposite, I thought I would need bigger main jets. Running 130 mains on my RS38's on my 1327 now:confused:
 
Here's the reason more air flow pulls more fuel through the jet making it rich. Had head ported on drag bike years ago same thing had to drop one size on main jet gained .5 second and picked up 10mph.
 
yep, bigger cams mean higher and longer lift = more fuel being drawn in.
surprisingly, i had to drop the mains when i went from pods to belmouths, for the same reason
 
Ok, thanks, I was worried something weird was going on. With the 130 mains, I am only seeing under 11-1 A/F at WOT above 7k rpm. If i open it up under 6-7k, the A/F dips to the low 9's. Cruise is 12-13-1.
Going to drop to 125's and see what change it makes.
 
gearhead13 said:
Ok, thanks, I was worried something weird was going on. With the 130 mains, I am only seeing under 11-1 A/F at WOT above 7k rpm. If i open it up under 6-7k, the A/F dips to the low 9's. Cruise is 12-13-1.
Going to drop to 125's and see what change it makes.
Click to expand...

Holy mackerel, I assume you plugs are blackish with those AFR's? If not is your sensor properly calibrated?

Remember if you run around with your O2 sensor in the bung all the time the unit has to be powered else it will ruin the sensor. Does it calibrate properly?
 
before I sold my stock 81 GS750E 16V, I put a stock 1100 intake cam from the 80-82 and I had to boost the main up 2 steps. It was already running a little lean because of a K&N filter in a closed air box, but with the cam it need the bigger main.

Otherwise it was all stock :confused:. Must be a complicated relationship.
 
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posplayr said:
Holy mackerel, I assume you plugs are blackish with those AFR's? If not is your sensor properly calibrated?

Remember if you run around with your O2 sensor in the bung all the time the unit has to be powered else it will ruin the sensor. Does it calibrate properly?
Click to expand...
My plugs look ok, the electrodes are not black. 99% of the time I am at cruise with A/F mid 12-13. Before the cam swap I was seeing 12.5 wot 7-9k rpm.
I dont run it without the O2 sensor powered up anymore. I emailed their tech support and they said if I dont get any error messages that I am ok. I can tell when it drops below 10, it chugs and misfires. These RS carbs go very rich when wot below 7k rpm, after that they lean out about 2 A/F steady up to redline. You cant just whack them open, you have to roll on the throttle.
 
gearhead13 said:
My plugs look ok, the electrodes are not black. 99% of the time I am at cruise with A/F mid 12-13. Before the cam swap I was seeing 12.5 wot 7-9k rpm.
I dont run it without the O2 sensor powered up anymore. I emailed their tech support and they said if I dont get any error messages that I am ok. I can tell when it drops below 10, it chugs and misfires. These RS carbs go very rich when wot below 7k rpm, after that they lean out about 2 A/F steady up to redline. You cant just whack them open, you have to roll on the throttle.
Click to expand...

You are supposed to look deep down inside at the base of the insulation for a rim of soot. Some people cut the plug to see down there.

I think I pretty much stayed above AFR 11 most all of the time the leanest mixture at mid range throttle

Using the AFR meter, you have easily become a real expert of RS roll on's
 
Did you degree those 1100 cams? I know from experimenting that a few degrees of cam timing can change jet requirements by a couple sizes.
Considering I cant see down there on the plugs, I can assume they are black. I am running d9ea plugs, maybe I should go back to d8ea:confused: Cheaper and easier to find locally too.
 
gearhead13 said:
Did you degree those 1100 cams? I know from experimenting that a few degrees of cam timing can change jet requirements by a couple sizes.
Considering I cant see down there on the plugs, I can assume they are black. I am running d9ea plugs, maybe I should go back to d8ea:confused: Cheaper and easier to find locally too.
Click to expand...

yes 0.340" cams are degreed a per Webcams spec. Don't know it right off the top of my head. I'm also running the recommended NGK Iridium plugs. I'm at sea level and when climbing to 6000 ft plus it really helps burn off the plugs.

BTW I'm running a 135 main with BS36's
 
posplayr said:
yes 0.340" cams are degreed a per Webcams spec. Don't know it right off the top of my head. I'm also running the recommended NGK Iridium plugs. I'm at sea level and when climbing to 6000 ft plus it really helps burn off the plugs.

BTW I'm running a 135 main with BS36's
Click to expand...
I meant the 1100 cam that you put in the 750.
Web says #223 (.340") cams are supposed to be degreed 105/107
 
gearhead13 said:
I meant the 1100 cam that you put in the 750.
Web says #223 (.340") cams are supposed to be degreed 105/107
Click to expand...

No I did not degree the GS750; did not bother as I was selling it. It ran well and ran better after splitting cases honing and new rings. Lapped the valves and put in a set of nice 1100 cams. It stumbled and hunted at 1/8 throttle until I boosted the main jet. No other changes.

105/107 sounds about right for the 1100.
 
Went from a 130 to a 125 and only dropped 1/2 an A/F, looks like I need 115's:confused:
 
Well, I am really confused. My log files show the rpm maxing out intermittently, mostly at high rpm. I am wondering if my non-suppression wires are messing with the innovate stuff or my rev limiter.
I didnt have any mikuni jets smaller than 125 so I put in DJ 124 (about 116 mikuni) and not much change in A/F.
Maybe its ignition related.
 
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I have d9ea plugs in it now I am going to put some d8ea ones in. Maybe they d9's are too cold?:confused:
 
gearhead13 said:
I have d9ea plugs in it now I am going to put some d8ea ones in. Maybe they d9's are too cold?:confused:
Click to expand...

I dont know but what you are doing is scarrrrrry.

I think you need and independent AFR measurement before going any further :confused:

With my change to 4:2:1 and ported head I dropped from about 142.5-145 down to 135. You are moving a long way further than that. I wonder if your carbs have a gas leak and so you are not affecting the entire gas flow as you think with the main jet?
 
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posplayr said:
I dont know but what you are doing is scarrrrrry.

I think you need and independent AFR measurement before going any further :confused:

With my change to 4:2:1 and ported head I dropped from about 142.5-145 down to 135. You are moving a long way further than that. I wonder if your carbs have a gas leak and so you are not affecting the entire gas flow as you think with the main jet?
Click to expand...
When I put the jets in I pulled the bowls and rechecked my float height. I really dont know unless my floats are not floating as much as they should. I turned the carbs on their side and tried blowing into the fuel line and the fuel valves seal well.
A gas leak from where to where? If the bowls filled too much it would just go out the overflow.
The acc pump is totally disabled as well.
 
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