Rich AFR, low hp

[crestview750f]

1982 CB750F SS, stock except for K&N air filter and Yoshi-style 4-1 pipe. I will be installing 900F cams and wanted to dyno before and after cam swap; hp was 44 @ 7,950, tq was 37 @ 4,100.  Unfortunately, the jets are waaaayyyyy too rich; 10:1 afr starting at 3,000 rpm. My thought: go back with stock #68 primary and 98 main jets. I had the carbs cleaned in June and the tech installed jets from a Dynojet Stage 1-3 kit.
Haven't dropped a float bowl yet but I'm expecting to find something much larger than 100 main jet. Although the needles now have e-clips, dropping the needle won't help how rich it is at WOT.

Your thoughts?

[TOOLS1]

To get an accurate comparison you should be using the stock tuning on your dyno tests. But I am really wondering why your mechanic thought you needed the Dyno jet crap in your carbs. Did he do any plug chops? You are in Florida as close to sea level as you can possibly get, why did your mechanic think the engine needed richer jets? If anything, it might have needed to be leaned out.
TOOLS    

[crestview750f]

The carbs definitely needed cleaning; #1 and #4 pipe were cold after starting until I dropped the bowls and ran a piece of copper wire through them.  13,000 miles and 32-years old, not a lot of fuel went through them and, probably, sat in the bowls for a while.  So, we cleaned them but the stock pipes were on the bike when I bought it.  The elevation in Waco is just less than 500' above seal level.

Thinking the mixture needed to be a little richer with the 4-1 pipe after removing the stock exhaust (4-2), the tech suggested (and I agreed) we should put in larger jets; the benefit was adjustable needles with the kit.  Now, at sea level, it runs way too rich; I mean you can see and smell how rich it is and was verified by the AFR; we went way too big on the main jet.  So, back to the drawing board with stock primary and main jets; plug chops with new plugs are in the mix.

Except for thinking about smaller jets as you said, I think I'm on the right track.

Thanks, Tools!

[TOOLS1]

Since most of the population lives below 2K feet above sea level, Honda tuned these bikes with the assumption that most would be sold at these elevations. The stock jetting should have been really close for sea level. Changing the exhaust rarely requires a jetting change, and the K&N filter should not have affected it that much either. A friend of mine just made the same mistake while preparing his bike for a trip to Baja. He thought he would need larger jets because he was going to be closer to sea level, but the bike did not need re jetted, and ran very rich.
TOOLS

[crestview750f]

Found the problem; #68 primary (stock), #130 main.  Needle is clipped 3rd from the top.  Just a little more rich than stock #98 (read: a whole lot more than too rich!).  

Will replace stock jets, re-dyno, get the numbers, and install the cams.  Redyno after that.  Updates in a couple of weeks.

[crestview750f]

I found a jet diameter cross reference, Keihin, Dynojet, Mikuni. If the #130 in there now is the Dynojet jet, the equivalent Keihin jet is #140. That's rich (the cross reference, too)!

[shinyribs]

It'll be interesting to see what the power numbers look like once you get the jetting all straightened out. Do you plan to go back to the dyno once it's done?

[crestview750f]

Shinyribs, that is the plan. Hard to brag about differences if based on what the the factory said and what I got; a more true before and after.  Not to mention the increase in power when properly jetted.

[crestview750f]

While I'm thinking about it, here's link to the jet cross reference chart I mentioned.  Funny, though; it's Honda ATV website!

Clicky here

[crestview750f]

Did a little troubleshooting today with a compression test; just to make sure the cylinders are healthy. 140, 145, 140, 140.  Using 14.7 ambient pressure x 9:1 compression ratio, these numbers look good. Now, to develop a leak down tester. That should make the fat lady sing!

[motogrady]

I messed around a bit.  On my 79f, stock air box with maybe 8 1/2 inch holes drilled in it, stock paper filter,
4 x 1 pipe, cleaned carbs 4 times, guitar string, acetone with 100 psi air, 75/110s and the bike lit up.

What do the plugs look like?

[crestview750f]

Plugs were light grey; you could see/smell the richness of the fuel.  AFR was 10.

Pictures of Stock and DynoJet jet needles.  Instructions were to install e-clip 3rd notch from the top (rich) but the 130 DJ jet is the same as the OEM 140 jet.

Thought some might be interested to see the OEM 53E jet needle and the DJ.  Notice the tips of the needles and taper.

[Re-run]

Not a dohc, but on my 78, I go for a very light dusting on my plugs.

[motogrady]

another thing I noticed when shaking mine down, was the sensitivity to battery charge.
When I found 2 burnt molex connectors under the battery box, fixed them, and threw a good slow charge on the battery, that seemed to help a good bit also.

If I did anything major to mine, it would be some aftermarket charging system, it's the other weak link
in these models IMO.

I've never dynod mine, but, after getting it sorted out, running and pulling clean, 52 mpg.

[crestview750f]

Spoke with Mike Nixon at motorcycleprojectdotcom. Replaced the K&N with stock paper filter; rejetted with stock 102 main jets and 53E jet needles; will dyno this week but accelerates and  passes 9500 rpm without a cough or hiccup. I think the dyno will confirm the power is there. Next step: 900F cam install, then back to the dyno!

[Re-run]

Yeah, I hear good things about the 900 cam in these.
I haven't heard anyone not like it! Who complains about a bit more power?

[crestview750f]

Good results so this will be my next to last post on the rich AFR; stock jetting (68/102 jets, 53E needles) rendered 56hp and 13.8 AFR through out range from 1/2 - WOT. Will now install 900 cams and rejet as necessary and add dyno sheet to new thread.  Dyno sheet will show orig and now results; will post dyno sheets tonight.

[Re-run]

I think this will be the first time someone has actually posted a dyno after the 900 cam swap. Cant wait to see it.

[TOOLS1]

I would like to see the results with just the cam swap before doing any jetting changes.
TOOLS

[crestview750f]

Dyno runs are original rich AFR and latest.  Lines on latest include 1/2, 3/4 and WOT.  I'm wanting to get the AFR right at all positions and will be using the CV chart also attached.

Tools1, once the 900 cams are in, we'll dyno before making any jetting changes; we have a good baseline now that is near 13.2-13.5 for power on the dyno in Milton.