after 9 years stock, my evaluation of Dave's Mods


33 replies to this topic
  • tgstoken

Posted March 08, 2008 - 11:14 AM

#21

With my uncorked, desmogged, Twin Air filter, Supertrapp Exhaust, Dave modded bike, I am running 60/160 jetting and it is near perfect. Plug looks black all around with a white-ish tip. This is at everywhere from sea level up to around 2,000ft. 650's are fun when riding with people on 250's and 225's....I just eat them on straight stretches.:thumbsup:

  • Purcell69

Posted March 09, 2008 - 03:36 AM

#22

Joe,

Dynojet numbers are different from Keihin's. I operate from 800' ASL to 2500' ASL with K&N filter, no snorkle, desmogged, and slight mods to the stock exhaust for better flow and sound. 55/158 Keihin jets with air screw at 2 1/2 turns out and slide drilled to 5/32 seems to work perfect for me. I am keeping the 58/160 jets in case I ever want to go with "full race" exhaust or operate at extremely high elevations.


Thanks Itchykawa. I had read about the difference in jet sizes in another thread. If memory serves, The DJ is two numbers bigger than Keihin, ie. 160 DJ = 158 Keihin. I had a MOD Fest yesterday and installed the DJ kit, pulled the snorkle off the air box and ground the headpipe welds. The problem is the DJ kit did not have the slow jet, so I ordered a 55 Keihin for it. As a result, I'm holding off on the Uni Filter and may put the snorkle back on until I get the slow jet installed.

What about drilling the slide with the DJ kit? The info on the jetting and carb side says not to mix Dave's Mods with the DJ kit, as the kit has a different spring that performs the same function as drilling, but then Martinfan advised just the opposite in another thread yesterday. I don't want to start a turf war, but I don't want to mess up my slide either.

-Joe

  • Purcell69

Posted March 09, 2008 - 03:46 AM

#23

If you go into extremely high altitudes, a 160 main will not help you at all. Remember, the higher you go, the leaner the mix, therefore, smaller jets would be needed.


I think you might have mis-stated yourself. The higher you go, the more you need to lean out the mix, hence the smaller jets, as you said.

As elevation increases, the air density decreases, causing a rich condition. This is why aviation gas has oxygenators added to the fuel.

-Joe

  • Itchykawa

Posted March 09, 2008 - 11:23 AM

#24

Thanks Itchykawa. I had read about the difference in jet sizes in another thread. If memory serves, The DJ is two numbers bigger than Keihin, ie. 160 DJ = 158 Keihin. I had a MOD Fest yesterday and installed the DJ kit, pulled the snorkle off the air box and ground the headpipe welds. The problem is the DJ kit did not have the slow jet, so I ordered a 55 Keihin for it. As a result, I'm holding off on the Uni Filter and may put the snorkle back on until I get the slow jet installed.

What about drilling the slide with the DJ kit? The info on the jetting and carb side says not to mix Dave's Mods with the DJ kit, as the kit has a different spring that performs the same function as drilling, but then Martinfan advised just the opposite in another thread yesterday. I don't want to start a turf war, but I don't want to mess up my slide either.

-Joe


I read a thread somewhere from someone who is running a Dynojet spring AND drilled slide with no problems. I THINK I even saw XRLDave recommend this to someone somewhere too - I even THINK I read a thread from Dave himself in which he claimed to be running a Dyno spring with a drilled slide. This all from memory and I could be mistaken. I do know this has been discussed before and you could probably find a thread on this subject if you were determined.

I would drill it - but that's me.

  • martinfan30

Posted March 09, 2008 - 11:27 AM

#25

I read a thread somewhere from someone who is running a Dynojet spring AND drilled slide with no problems. I THINK I even saw XRLDave recommend this to someone somewhere too - I even THINK I read a thread from Dave himself in which he claimed to be running a Dyno spring with a drilled slide. This all from memory and I could be mistaken. I do know this has been discussed before and you could probably find a thread on this subject if you were determined.

I would drill it - but that's me.


When I still ran my stock CV carb, I installed the complete Djet kit AND drilled the slide. I had great throttle response. As good as you can get with the CV Keihin.

The FCR is even better yet IMO.

  • Itchykawa

Posted March 09, 2008 - 11:31 AM

#26

If you want to go with a "full race exhaust" a 160 main will be too lean IMO. I've got my homemade headers which have a higher rate of flow than stock and probably most aftermarket headers. After installing my homemade headers, the engine ran kinda lean and I did lose some bottom end, even with a DynoJet 165 main. I didn't want to go to the next higher up main which more than likely would have had to be a 170. So, instead, I raised up the needle 1 notch and that did the trick. The engine has run beeeeautifully ever since.

If you go into extremely high altitudes, a 160 main will not help you at all. Remember, the higher you go, the leaner the mix, therefore, smaller jets would be needed.


Oh $#!+, you are right! I need to rephrase that. My BB-in-a-boxcar brain fails me from time to time. Thanks.

  • dldavis_66

Posted March 09, 2008 - 05:13 PM

#27

I think you might have mis-stated yourself. The higher you go, the more you need to lean out the mix, hence the smaller jets, as you said.

As elevation increases, the air density decreases, causing a rich condition. This is why aviation gas has oxygenators added to the fuel.

-Joe


:thumbsup: I stand corrected. :eek:

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  • dldavis_66

Posted March 09, 2008 - 08:20 PM

#28

:thumbsup:

Thanks Itchykawa. I had read about the difference in jet sizes in another thread. If memory serves, The DJ is two numbers bigger than Keihin, ie. 160 DJ = 158 Keihin. I had a MOD Fest yesterday and installed the DJ kit, pulled the snorkle off the air box and ground the headpipe welds. The problem is the DJ kit did not have the slow jet, so I ordered a 55 Keihin for it. As a result, I'm holding off on the Uni Filter and may put the snorkle back on until I get the slow jet installed.

What about drilling the slide with the DJ kit? The info on the jetting and carb side says not to mix Dave's Mods with the DJ kit, as the kit has a different spring that performs the same function as drilling, but then Martinfan advised just the opposite in another thread yesterday. I don't want to start a turf war, but I don't want to mess up my slide either.

-Joe


Drillin them slide holes out to 5/32 aint gonna hurt your slide one bit,with or without the DJ Spring. Fact, I gots mine drilled out with the DJ Spring and my sickle runs real nice. Yeee up.:eek: DJ kinda stickin their foots in they mouth saying ya caint do Dave's Mods with they kit, yeah huh.:D

  • durandal

Posted March 09, 2008 - 08:21 PM

#29

I'd just like to add my 2 cents: I have done half of Dave's mods.

I don't have the jets yet, but I drilled the slide, raised the needle and there is already an aftermarket pipe, filter and no snorkel on the bike.

Any differences? I can't say for sure. I think so. Last week the bike went above 275 on the freeway, but today it stayed at 250. Was it warmer last week? yes. Is any of this any use to anyone? I have no idea.

I also replaced the stupid phillips-head screws on the float bowl with allen head screws. (I just discovered Ace hardware. I'll be going there often in future!).

This whole process has been complicated and delayed by a lack of tools. I just moved to the US some 7 months ago, and have started from absolute scratch. Everything has had to be purchased from zero (including the bike, obviously). But things are going smoothly now. And I hope I can get away somewhere on the bike for Spring Break– on a properly jetted mile-eating machine.

Here's a bit of bizarre trivia: the previous owner, for some strange reason, rejetted the bike *leaner* than stock. Main: 148. Pilot: 50 S.

This with a Supertrapp IDS2 race core and no discs or end cap, K&N (which I quickly replaced for a UNI), no snorkel.

Granted, this is Albuquerque, 1600 metres above sea level. Not much at all, but it might warrant a tiny change. But that much? I question his his judgement!

d.

  • dldavis_66

Posted March 09, 2008 - 08:35 PM

#30

Here's a bit of bizarre trivia: the previous owner, for some strange reason, rejetted the bike *leaner* than stock. Main: 148. Pilot: 50 S.

This with a Supertrapp IDS2 race core and no discs or end cap, K&N (which I quickly replaced for a UNI), no snorkel.

Granted, this is Albuquerque, 1600 metres above sea level. Not much at all, but it might warrant a tiny change. But that much? I question his his judgement


I reckon that all depends on where this dude was from. He could been ridin up in them hills way up yonder over 3, 4 even 5000 feet. A 148 main would do just nicely thay way up. I knows Albuquerque aint totally flat. I thinks thinks they got at least one hill that might be up around 4 or 5 thousand feet. I don't know how many meters that is, but I'm sure it must be a bunch.

Yeah, you better get yourself some bigger mains, prolly a 160, maybe, even a 165 if you get some aftermarket headers, down where you is. A 55 pilot would do you good too.

  • martinfan30

Posted March 09, 2008 - 08:42 PM

#31

Ok, I live at 4300... Stock jetting(152/50?) was still a hair lean here. A 148 main might work at 5500 ft. plus. Although I ran 158/52 just fine at 10,500... A bit rich but ran ok.

  • durandal

Posted March 09, 2008 - 09:25 PM

#32

I consider the bike to be lean as it is right now. Excessive highway temps (when I myself am freezing), ample popping and sputtering on decel, and less power/torque than I expected, judging from people's descriptions (I'm coming from an XR250R, and yes, this is my first 650).

I should, of course, check the plug. But so far I've been lazy. :-P

d.

  • Purcell69

Posted March 09, 2008 - 09:33 PM

#33

Well, I put the carb and airbox back on the BRP today. I was a little concerned about the slow jet being lean (stock) with the air box desnorkled, the DJ kit installed and the head pipe weld ground, so I left the stock air filter in for a test run. Keep in mind, I have not drilled the slide...yet. I still have the stock exhaust until I get the E2.

Even still, it runs like a different bike! The throttle is pretty snappy with the DJ spring and there is no problem at all with lofting the front tire using stock gearing and a little gas. The engine pulls a lot harder now than it used to. There is a very marked improvement. It is easy to feel in the seat and the handlebars.

On the interstate it seemed to flatten out at 90-95, but pulled nicely up to that point. Perhaps with the E2, Uni installed and rejetted to match, it might pull a little harder in the top end. Right now the needle is set in the middle (3rd) position. Either way, I am a happy guy! When I install the E2, I'll go up to the DJ 165 main, drill the slide and install the 55s jet.

It is safe to say that I am a big fan of Dave's Mods, no matter how they are accomplished.

-Joe

  • durandal

Posted March 23, 2008 - 10:20 PM

#34

Right. I've installed the new jets.

55s pilot, 155 main. I do have the 158 and I'll try it when I'm bored.

I'm running a Uni filter and a disc-less race core Supertrapp IDS2 exhaust. My altitude is around 1700 m, which isn't much, but I thought I might go down 3 points on the main just to see what it was like.

I've taken the bike out for a spin, and the popping on decel is completely gone, and there bike feels like it has more punch. Perhaps not more power, but like it finally came out of puberty and it's voice no longer breaks. Sorry if that was an incomprehensible metaphor.

I disregarded the graph I usually use to calculate jetting changes. It's from my XR250R shop manual. Assuming a 158 main is what's needed at sea level with an uncorked bike, my altitude and air temp would suggest a 152 main according to this graph.

Posted Image

Anyway, it's easy to over-think things. Good thing is, the bike runs great now.

d.





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