Fix the hesitation-something different

[wayne]

Something a little bit different but it worked. The short and sweet:

Try a bigger SECONDARY main jet (remove large brass nut UNDER the carby and unscrew jet, it falls out, easy).

Original is 180, I used 185 but a 182.5 might be better.

Wouldn’t run with a 190.

Jet number is Mikuni:

N100/604

showandgo.com.au

That’s the short version, the longer version follows.

I’m having trouble sorting an A model’s hesitation.

I’ve tried all the usual suspects- NOS carby cleaned twice. Acc Pump tried at 28° and 35°. PV set precisely at 35°, tried NOS stock filter, tried Jess’s replacement filter. Tried 5° ignition, 8.5° and 10°. Tried bigger primary main jet (95), tried servicing the enrichment mechanism, also disconnected the enrichment mechanism and plugged the vac line and even fitted the mechanism with a device that allowed me to manually close the valve and enrich the circuit. While the characteristics changed slightly and the hesitation moved, nothing had any effect WHATSOEVER on the strength of the hesitation.

After rereading the carby chapter in the book for the tenth time, I decided that a secondary main jet change was the only practical option left.

I fitted the bike with a 190 SMJ (up from 180) and a 95 PMJ (up from 90 or 87.5)). I ended up walking home from that one. Bike went 500 metres and refused to run.

I did nothing but return the jets to 180 and 90 and it fired up and I rode it home.

Next I tried just the SMJ 185 and 90 PMJ. This had a significant effect on the hesitation.

For some reason, it will still hesitate as horribly as ever if you launch off hard in first gear. But after that first hesitation, it runs with no hesitation but you can occasionally feel a surge of power as the secondary comes in, more so than normal.

I tested the bike accelerating very deliberately with the throttle wound to the stop from 2,000 to 4,000 rpm several times in all gears and it pulled through with no hesitation at all.

I think that a 182.5 may be the go, perhaps combined with a 92.5 PMJ to lessen the effect of the slight power surge.

I have much more experimenting and riding to do to confirm this, but I put it out there so that perhaps someone else may be able to confirm my findings or otherwise.

I’ve said before that tuning RE5’s is more like a recipe than a formula and I've still haven't worked it out. Some stuff that works on one bike doesn’t work on another. You seem to need to tweak each machine a little differently to get the taste just right. And I was getting close to the tear-your-hair-out stage (just slightly down from the drive-a-screwdriver-into-your-brain frustration level).

Wayne

[ap951]

Thank you Wayne, your report & information has a lot of value to me right now

Bill

[ziggystardust]

Keep up the good work Wayne, you can do it, don't let it beat you.



Z

[t140v]

Evening All,

I have replaced the primary jet with a 97.5 kept the timing 10 degrees btdc dont have any hesitation. Engine ran smoothly through the rev range.

However the battery on the bike was not very good and was having problems starting the bike even though it had been on the optimate all week, when it got going I went out for a ride and the engine was back to square one very rough and hesitating around 3500rpm.
After fitting a new battery the engine was back to smooth through the rev range once again, something else to take into consideration if your using an old battery on your bike.

Regards Stuart.

[wayne]

Thanks and interesting. It does have an old battery but I do have a brand newie in the other bike. I'll do a swap with the standard jetting (that gives me guaranteed hesitation) and see if that makes a difference. Didn't think of that ingredient.

Of course the other bike has an 87.5 PMJ and runs perfectly, can regularly get 46 mpIg and can do over 150 miles before a refill. Damned if I know.

Wayne

EDIT: Further to your suggestion re the battery, I do have an A grade racer acquaintance with decades of experience who often tells me that 50% of carby problems are actually ignition. He's not referring specifically to RE5's, it's a general comment.

[pmcburney]

Hey Wayne,


You know, I gave what you're doing some thought a while back.

I studied the carb flow diagram for a while and it seemed logical that a larger SMJ may make a difference as the PMJ is fed via the SMJ.

I never tried it out.

It seems from your experimentation that it could have some merit - I'll gets me a couple of jets and give it a go.

Nice work, yet again!


Cheers
Paul McB

[wayne]

Yes Paul, I know what you mean. I think we all have a lot of musings turning over re these bikes. Dan independently posted about the enrichment mechanism with a week or two of my first off-the-board musings about it. That SMJ has been in my thoughts for a while as well.

Saturday I'll try the battery with stock jets, battery with 185 jet where I was still getting the initial hesitation and I've now got the 182.5 and the 92.5.

Sunday I'm hoping for a 250 klm round trip to the VJM to give it a good run once Saturday's testing comes up with the best option.

[ap951]

that 250 klm trip might be just what the old girl needs Wayne.

It sounds like it hadn't been used much until recently. I bet she runs better after the trip

Bill

[wayne]

I've thought that Bill, perhaps just get some miles up on it. Will report.

Wayne

[hunter]

Hi Wayne,
Question with out fear or favour, hehehe. This is flat spot hesitation you are talking about? NOT the grining thru that range?? My A does not have hesitation but does have the grinding, only on hard acceleration in high gears when the engine cannot run quickly thru the offending rev range. Gentle to firm is ok and in low gears under hard acceleration it is ok too when it can rev thru quickly.
I got bigger primary main and bigger secondary main, but I cannot remember what sizes I got in. I will have to check them

[hunter]

I agree whole heartedly with that observation Wayne about ignition causing problems too. I have wondered about the auto advance unit and its effect. I don't know at what rpm the ignition advances under centrivical force. mmmm I think it should be much before 3,400 rpm but I not sure. But if the unit is sticky or worn it could add to fuel mixture issues.

[wayne]

Hi Kim and firstly, did you see the note about the Sydney dyno day.......I sent you a direct email but not sure about your address these days.

Secondly, I'm talking about the hesitation- nothing like the grinding. Every RE5 I've ridden has the grinding harshness somewhere between 3,500 and 4,000. My RE5M is fairly harsh in that area and if you combine it with a steep hill, the engine seems sometimes reluctant to accelerate through it. I think it was Dan who commented about fitting a stronger tensioner on the primary chain as the harmonic ends up being transmitted through the primary drive and beyond. That apparently helps. I personally don't believe you'll ever get rid of that harshness, you just might be able to reduce its transmission.

No, this hesitation is a unmistakeable "cough" that stops the engine dead for a second and will almost spit you over the bars when it's really bad. Generally somewhere between 2,800 and 3,300.

Dan has also commented about ignition advance helping with the hesitation. Search his posts as he mentions which springs etcetera.

PS Show off.........I see your list of bikes

[hunter]

Depends on date and timing of Dyno day, I try to find 2 mates and bring all 3 rotaries.

[wayne]

Just an update after 200 miles of testing in a one day ride and several combinations of jet changes.

Results with the SMJ were not as clear cut as the other day. It seems that a larger PMJ has more of a positive effect on hard acceleration, say from a standing start. I don't go beyond 3,500 so that each gear change drops you back into the "zone".

It also seems that the large SMJ has more of a positive effect on "roll-on" acceleration. With just a larger PMJ, it would accelerate from a standing start in first gear with no hesitation but would be cranky cruising around 45 to 50 mph (approximately 3 to 3,300 rpm) and would hesitate winding the throttle on. With a larger SMJ, cruising in that area and even higher seemed smoother with less tendency to cough when the throttle was suddenly snapped open. Sort of makes sense.............

More playing to do.

PS It was interesting to find that while riding I could put my left hand down in front of the carby and get one finger on the secondary actuation arm and feel it move around. Not sure what it tells me right now other than it certainly is related to the hesitation rpm band.

[wayne]

Okay, I've done 500 miles of testing with numerous PMJ and SMJ combinations and have arrived at a conclusion. The last 200 miles of testing was 100 miles with a single combo and then 100 miles back with a different combo. A decent test in my opinion.

I'm afraid that I believe the only reason I got the SMJ to make a noticeable difference in the first place is that I hadn't tried a big enough PMJ (I stopped at 95). I was reluctant to go bigger but after chatting with hunter (Kim), I decided to go bigger on the PMJ as others have been successful with 100 jets and even bigger.

The 100 PMJ made a big difference and the bike ran on the 100 mile test just shy of being perfect. It has no hesitation through numerous drag-strip style starts. Going pretty hard through some low speed twisties (all 15 to 30 mph corners) which keeps you transitting "that" rpm zone it would occasionally give a hint of a hiccup and I really mean just a hint- hiccup is too strong a word. All in all, I'd call it 95% and this was backed up by another RE5 owner who rode it some distance in different conditions.

Now I had it almost sorted, I changed from the PMJ/SMJ combo of 100/180 to 100/185 and rode back 100 miles. Unfortunately, the bigger SMJ did nothing to fix the very minor remaining glitch. The only things that it did do and was quite noticeable was that I needed 3/4 more turn in on the idle stop screw and it made the bike run noticeably cooler despite 10 deg C higher ambient temps. In 1000 miles this bike always sits slightly to the right of the mid mark and with the 100/185 combo it came back to the left of the mid mark where every other RE5 I've ridden tends to sit at highway speed.

So, if you can't get a 95 or 97.5 PMJ to work, go bigger, 102.5, 105 even. I might still do that myself.

BUT, if all else is failing, try a bigger SMJ. It may help YOUR bike. They are all different and I'm getting comments to that effect from my "newbie" RE5 friends as they ride different bikes and see this for themselves.

I'm just very disappointed not to be able to get this one sorted with stock settings. Maybe another 10,000 miles, about how long the other one took