Power band of Jim Lomas exhaust on GT750

[smokey]

Hi all,
We just put a Jim Lomas exhaust on our GT750A. The bike is stock except the exhaust.
just wandering what sort of power band to people see with this exhaust.
the bike seems to come on the pipe about 3500RPM and pulls hard till about 6000RPM, where it looses noticeable power.
I'm not sure if that fall of is a characteristic of this exhaust design, or if we still need to futz more with jetting.

thanks for the help!

[tz375]

Hi Smokey,

You are the first person I know that has a JL exhaust, so I have no hard data to work with. That pipe is very long and with stock porting I would expect it to peak early. That, of course, is just speculation based on playing with a lot of different pipe designs.

If you have a dyno shop close by, I'd recommend that you get it dialed in on the dyno. Have them run it with exhaust gas analysis wide open to get main jetting correct and then have them do a couple of runs at partial throttle to see how far out it is where you normally run.

You have any pics of the bike with hose JL pipes fitted? How well did they fit? JL pipes look awesome.

[smokey]

Thats a good point, I just assumed that a wide band O2 would foul out in the exhaust stream, but having that info would be really helpful. Its getting so cold here in Philly, its making it hard to tune for warmer days the bike mostly gets used in.
So our experience with the Jim Lomas exhaust... We ordered the pipes direct from JL. There is a note on the website about “please allow 14 to 21 days for delivery” , I'm not sure if they were backed up with work, but they never contacted me to say they would be behind on delivery. So many emails and excuses later, and a threat to bring it up with Paypal (which has 45 day window to file grievances) The pipes finally shipped on day 40.
The pipes arrived quickly via TNT shipping. We needed to be home to sign for the pipes. Fortunately there were no customs issues, as I read horror stories on line about TNT and how they handle that. The pipes are quite a thing of beauty as appearances and TIG welding go, as for fit and installation, thats a different story. Its more or less up to you to figure out how to fit the pipes to the bike, no diagrams or instructions included. A bag of random hardware is included, but we needed to make extra spaces and add washers to get the pipes to clear the bike.
The center stand needed to be removed, to fit the pipes. The left pipe fits and clears the mechanicals quit easily with a extra 1/2” spacer, but its only really only mounted on the original rear rubber exhaust mount, so it has quit a bit of movement due to that and flexing in the bracket welded on the actual exhaust. I'd like to add a extra bracket between the pipe and the unused center stand mounts to firm that up, but my Lincoln buzz box is not up to that task!
The center and right pipes were a pain to get to fit. Lots of experimentation with spacers was needed to get the pipes to clear the engine / frame. Biggest issue is the right pipe interferes with the travel of the rear brake leaver. We needed to bend the leaver out to get more clearance and adjust the pedal higher than I feel is comfortable. What helped the most here was to replace the pin between the actuation leaver and the cable with a precision .25” dowel and drill the clevis and leaver to accept this slightly bigger pin, which got rid of most of the slop in the system.

Over the stock pipes, it feels like there is 10 or more HP gain and they have a good sound. I swear in 1 and 2nd gear the ft end is pulling off the ground, but the 15:44 sprockets helps that too Like I said before, we are still in tuning, and trying to understand the fall off in power above 6k. The bike was very lean on the pipes originally and we changed jetting to 117 mains and the needle on the richest position + .5mm washer, and I feel even bigger main is needed since it feels lean up top.
I was hoping to get jettting sort of dialed in before the cold, as this bike needs crank seals, which is this winters project. I rather smoke a piston now, vs after we fix the seals and likely give it a new set of pistons and a re-bore. Hopefully I can get more photos today, but here is one I already got of our project with the JL expansion chambers.

[Barry S.]

I thought he was talking about a 3 into 1 pipe, didn't know they made 3 into 3, look great.

[tz375]

Seriously nice looking pipes.

Yes an O2 sensor will get fouled pretty fast on the street, but dyno guys us a long sniffer and it's only sniffing for a short time on your bike. I have O2 bungs in different pipes but the sensor doesn't last any time at all.

With Jemco pipes and UNI filters I think I have 122.5s in now but needles in stock position. Get full throttle high revs set first and then mess with lower revs (lower slide) and then use float levels to fine tune the bottom end of the power band.

I have richer needle jets in mine, but I run race fuel and it needs to be richer than street gas.

Why is there a drain tube out of the oil pump housing? Oil leaks there are usually from too much oil in the transmission or blown crank seals. The latter won't be helping with power if it's a problem.

[smokey]

Why is there a drain tube out of the oil pump housing? Oil leaks there are usually from too much oil in the transmission or blown crank seals. The latter won't be helping with power if it's a problem.

Yes, agree, the bad cranks seals are not helping tuning. They need replacing. But for now, that keeps the oil off the rear tire and let us figure out if we liked the bike enough to spend the bucks to do all that work, which is a astounding YES ...

.

[Craig380]

They look VERY sweet

As for the fitting, as the inventor of the expansion chamber, MZ's Walter Kaaden once observed: "You will know when you have the correct pipe design, because it will be impossible to fit it to the bike without it dragging on the ground, burning the rider, or forcing the relocation of a major component."

[tz375]

Why is there a drain tube out of the oil pump housing? Oil leaks there are usually from too much oil in the transmission or blown crank seals. The latter won't be helping with power if it's a problem.

Yes, agree, the bad cranks seals are not helping tuning. They need replacing. But for now, that keeps the oil off the rear tire and let us figure out if we liked the bike enough to spend the bucks to do all that work, which is a astounding YES ...

.

PM sent with data on those pipes. When it gets warmer and you have a chance to get the crank rebuilt, it should run even better. We wend ours to Bill Bune in MN, but you have Paul Miller close by and that might be an option.