I finally got around to trying something I'd been wanting to do for a long time..

I removed the rod the red arrow's pointing at along with the rubber boot that goes with it-pulling it straight up and out, then capped off the brass tube the lower end of the boot slides over with a small vacuum cap to disable the accelerator pump linkage and remove any influence the AP might have while looking at a/f readings at various part throttle settings.



Not only was it easier to get true part throttle a/f readings without having the AP shot making the a/f ratio go rich-the bike seemed to run just as well without the accelerator pump! Maybe even better..?


This opens up (again) the possibility of using the cheaper TM36-2 carb that doesn't have an accelerator pump, but as klx678 and I discussed, I think it measures out differently and would be much more work to fit. Plus it uses different series needle jets and needles.

So, I think next time I have the carb off I'll put in the leanest AP nozzle I have (30) and adjust that black allen set screw you see aiming downwards thru the carb lid just about all the way down, so the AP delivers the minimum shot of gas. I don't think any more than that is needed.

For now though I'll just leave the AP disabled and ride it around some more. So far though I haven't noticed any sacrifice without the AP.

 

This is... amazing? hilarious? awesome? All of the above?

I'm on the fence about getting a pumper carb. I've remained skeptical about true power gains vs. perceived gains due to throttle response, and I don't want to deal with re-tuning for no good reason.

But yet, everyone says, gotta have the pumper carb.

And now, here you are, deliberately crippling the accelerator pump on a pumper carb.

To be blunt, I've found your testing a little erratic and lacking in follow-up, verification, multiple runs, etc... But I will say one thing for sure -

I like your style.

 

I will add that while idling (which is set a little high/but not much) on the stand there is a slight bog if I wick the throttle without the AP connected; but if I raise the idle at all-even just a hair with the throttle before wicking it, there's no hesitation when cranking the throttle. Only from absolute idle.

I crippled it to get better a/f readings straight from the internal jetting rather than what the AP was contributing. That worked very well as the a/f ratios indicated were much more steady.

I think the TM36-2 air cleaner boot bell is 1/2 inch larger diameter than the TM36-68 for starters, so connecting it to the air box boot could be a problem. I posted links to dimensions for both carbs previously. All in all it's probably easier to buy the TM36-68 when you figure installation hassles for the TM36-2.

 

If you read my story about installing the air box boot improperly on the CVK, you'd see where (evidently) the stock carb can be within .25 sec of the TM36 in a 1-4th gear sprint if that stock carb is given enough air.

I'll probably delve into that some more just to see how the times drop for the CVK if I add a mid-boot spigot/hose/and filter combo to allow more air into one of my extra air box boots.

 

Richard, I think you'll notice the accelerator pump plays a bigger role in off road conditions. When you're under a load in herky-jerky situations where you need the pickup and boost of the pump, that's where it shines. A carb like most of the ones that come on motorcycles will still draw fuel and operate without a pump. The pump just gives that little extra punch at more critical times. If it came on like a supercharger or a shot of nitrous, you'd often lose traction at critical times while riding off road.

 

No need to be pointing out random possible uses for a carb with an AP.

Disabling the AP was a quick way to ascertain part throttle a/f ratios and can easily be reversed. Now that I've tested without it though, the evidence is that very little if any extra shot of gas is needed for this carb/engine combo.

At low speeds with this engine added power from the AP shot isn't going to come on too strong no matter what you do because there isn't that much HP waiting to be had from the little extra squirt anyway. The a/f ratio will almost certainly go rich briefly no matter how small the nozzle or how brief the shot of gas, which could as much cause a stumble rather than a brief boost in power. Especially at low speeds; where I'd rather have power control at the throttle than the injected power adder of an AP.


I'm not advocating that people disable their AP, but after personally testing without it, I would suggest that the pump shot be set to minimum because it is mostly superfluous on this engine and 99% of the time it will cause a momentary a rich condition.

 

I'm anxiously awaiting you going to big bore, and then testing TM36 vs. CVK... I can't decide if I want you to find gobs of power so I can go buy a pumper, or if I want you to find not much so I don't have to!

 

Everyone says the bigger bores are the quickest way to substantially more power, and there are already 351/TM36 combos afoot here. Though I am tending to think the long intake tract is holding back the CVK a bit, where that same length is of benefit when using the 36mm.

 

Richard, I thank you profusely. I do appreciate what you are doing and as I said, I do follow it.

If I remember right the measurements are very close and should fit, but I'll have to check on it. There is currently a thread on the Thumpers section where a rider is doing a Mikuni 38 round slide on a KLR650 and of course they do them on the SR/TT/XT500, but I'd do a flat slide.

I'm thinking I'm going to take the chance with the TM36-2. I'd have to screw with jets either way and might be able to get some information from one of the vendors.

 

Mark, I'd say look up the ID of the most popular needle jet (P4 or P6 etc) that's used here in the TM36-68, and the OD of the needle; then try and duplicate the resulting orifice size those two produce and duplicate it with similarly matched needle and needle jet in the series the TM36-2 uses for starters..