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94 XR628 HRC - FCR Carb Kick Starting Woes

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Hello All,

I recently posted my finished build for a XR600 scrambler/tracker.

Found here:

The engine mods include:
HRC Cylinder and Cam
Compression Ratio 10.5:1 - XR650L JE Slug
FCR Carb
XR's only header and supertrapp pipe
K&N filter (no air box or anything - just strapped straight onto the carb) 

Now my current jetting is:

42 PJ
158 MJ
68 Starter (what came with the carb)
NCVT needle 3rd clip
I essentially followed DOT-COM's jetting
The leak jet is also stock
Pilot out 1.75 turns.

Now I've searched the web/forums and couldn't find anything that resembled my problem... this bike is an absolute monster to kick start. I'd be kicking it close to 20 times to get any life out of her. If it does start, it would idle for a few seconds and then 'puff' and die. Eventually I'd get it warmed up but if I clicked it into first and the idle dropped too much, it would die again. Once warmed up, it would ride fine - strong pull but definitely not wheelie worthy... and would pop on decel.

I cleaned the PJ and MJ recently and tried again. Still no love. I do notice that when I kick it over, the engine would just thump once... as if it doesn't even turn over multiple times.

Now here's the interesting thing... I put the stock OEM carb in: 62 PJ and 152MJ. Chock on, two kicks and BAM!! fires up really well. On failed attempts when kicking it over, I can feel the piston at least complete a couple of cycles. Much different feeling in the kicker.

I live in Oz and at sea level. 

Now before I go out and buy jets etc, has anyone got any ideas what to go is?
My first thought is the PJ may be too small for my application with the open air filter and larger slug/compression.
What about the the PAJ?

Any help would be much appreciated. I spent too time on this bike to go back to the OEM carb lol!

Thanks guys!
 

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When you do get it running and fully warm with the FCR, do the idle mixture screw adjustment procedure. That will indicate whether your pilot jet is correct.  You may end up needing a #65 pilot jet.

These engines all have a lower idle speed when cold.  It's normal to turn up the speed during warmup, then back down when at full temp.

The on-off enrichener choke of the FCR is not very civilized.  My technique is to start the bike on full choke, then after maybe 30 seconds or a minute of warmup I manually hold the choke in a half choke position for a while.

Beware of twisting the throttle while kicking.  With a pumper carb, you risk flooding the engine, and then it will be very frustrating to start unless you recognize what has happened and do a de-flood procedure.  My technique is to squeeze the front brake while kicking, which prevents accidentally turning the throttle.

Edited by heart_of_darkness
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Im at sea level with a 628 10.5:1 and a decompless cam, xl headers, powercore 4 and an fcr39 and my pilot is 45.

Yeah HoD, I hold half choke for a second too. Depending how cold out it is. But never just straight push it to the off position quickly

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Thanks guys for the response.

HoD - you recommended a pilot jet #65. Wouldn't that be overkill?

The HRC cam has the auto-decompressor. I honestly don't mind it. Just wait for the click, use the manual decomp to go past the stop and kick away. Eventually I may remove it.
I was thinking going up to 45 as per the above response from Notorious.

I've got plans to purchase:
Pilot Jet: 45, 48 and 50
MJ: 160 and 165

I'll also plug the leak jet and make sure the AP is set up correctly.
DOT-COM's runs a 45 so that will be a good starting point. We'll see what going up three sizes will achieve.

I'll report back in a couple of weeks.

Cheers!

 

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Just an update on the investigation.

So I ordered a few jets online but the package was never delivered.

Nevertheless, I knew something wasn't right with the bike as it started before with a 42 pilot. So after tinkering around and swapping between carbs, I found out that the pilot circuit was partially blocked :(
I did install an inline filter but the carb was hydroblasted... so I'm guessing a bead of glass may have been stuck in there. This would explain why she never kicked over more than once. It just kind of 'thumped' when kicked.

Once going, I took it for a ride and had her warmed up. Did the fuel screw adjustment as per the usual and found the following:
1. At 1/2 turn out, the bike died
2. At 2 turns out, there was no noticeable increase in RPM

So I gathered this would indicate that the pilot is of correct size. I also noticed that the popping on decel was less now that the pilot circuit was clean. I guess if I ran a 45 pilot it would help alleviate this further.

Finally, I also plugged the leak jet as a test. As mentioned by others, this considerably increases the AP duration but I also noticed that even at very slow turn of the throttle, the fuel would still pass out of the AP nozzle. I gathered that the bypass was working but the plugged leak jet allows for no fuel to return hence forcing fuel out of the AP nozzle even at slow throttle rolls (please correct me if I'm wrong). This in my opinion would create an overly rich condition. So I managed to pick up a size #40 (very hard to find the #35) and I'll go from there. Other than that, the bike revs freely. No throttle wheelies though... but it has been lowered 6 inches all round with 15/45 gearing. Also doesn't help that I weigh 150 lbs. The slip of the clutch does the trick :p 

I'll still test a size 45 PJ and 160 MJ when I manage to get it.

Thanks again everyone for the assistance.

 

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Just so were clear.
The leak jet LEAKS the amount of fuel reserved in that spring loaded diaphragm WHILE throttle starts turning making all the fuel leave the nozzle in the carb bore. So not more pressure or harder squirt in any way. But longer. The reserve cant LEAK anywhere else so the whole diaphragms amount comes out the nozzle.
This is like the first 16th to 1/8th of the throttle turn.
Doesnt make a rich condition. Ride the 42 with a fresh plug in, Ride the 45 with a fresh plug in. Compare the plugs.
Youll find out easy if youre too rich in main once you cruise fifth and full throttle it.
160 was too rich for me with stock airbox, xl header and powercore 4.

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Yep, you are correct with the AP duration with a smaller leak jet.

I read this on another forum not long ago and it said: "A slow twist of the throttle will push a small amount of gas through the leak jet (which is the path of least resistance) and almost none will make it through the passage into the venturi. On the other hand, if you twist the throttle quicker, it tries to force more fuel through the passage which cant all go through the leak jet, so the rest flows through the whole passage and squirts into the venturi".

Hence to my understanding, if you block the leak jet, even at very slow throttle twists (i.e. regulating speed on roads/weaving traffic etc) it will continue to force fuel out the AP nozzle constantly as it has nowhere else to go (it'll dribble out and not squirt). Wouldn't this then be adding unnecessary fuel when just lightly cruising around and twisting the throttle a little? Hence my reasoning behind making it rich across the board if doing do.   

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No matter how you twist the throttle, the rod lifting lets off pressure of the spring loaded diaphragm. Do hard throttle or soft throttle the squirt happens. Theres no slowing down the squirt. Just control over the length of squirt duration.

Basically, youre motor will drink that. Its not rich if you full throttle it and give the motor a mouthful of air with no gas. The purpose of the AP. Were talking split seconds of hesitation vs response. A squirt happening longer, to its longest, is still not enough to make it run rich. The way an xr drinks it would have to never stop squirting to be rich. You need to focus on jetting not focus on your AP. Theres way more into the jetting factors.

Leave leak jet plugged. Main thing is does squirt hit throttle slide? Yes-bad. No-youre fine.

And theres never a dribble out. The nozzle hole is so small, the diaphragms clearances are tight. Pressure is always there. If you had two pots and poured coffee and the coffee pot had two holes. One pot was 1 cm one pot was 1". And you poured two cups of coffee with the 1cm hole and one with the 1" hole, did you fill up the coffee cup before it leaked out? Youre not pouring harder, just your pot holds coffee longer so theres more to pour. Not at once, pump faster, but squirt longer time cause it doesnt have a 1" hole to leak out of. It only has a cm hole

You could do nothing to your AP and still have the task of jetting correctly.

Were talking like the first 16th of throttle. Youll never use AP while cruising

 

 

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Thank Notorious for the explanation. Much appreciated.

I now understand where you're coming from. I was playing around with the carby off and swapping leak jets around and was able to visualise it.

The leak jet is plugged. The AP doesn't strike the throttle slide so we are good on that front. I've placed an order for a 45 PJ and 160MJ.

Just out of curiosity, what starting procedure do you use to kick it over? Do you simply twist the throttle a couple of times and kick it?

I currently hold the manual decompression and cycle through around 10 times (no throttle or choke and with the switch off). Then I find TDC, twist the throttle once, choke and then kick it over. Typically it takes me 3 or 4 kicks. I'm still refining the process.

Cheers

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Sounds good just stop twisting the throttle so much.Squirt squirt squirt squirt squirt is all thats doing. Why dont you just take the plug out and fill with gasoline? Get jetting right. I dont even touch my throttle. I just turn up idle 1/4 to 1/2 turn and pull choke. The AP is really only something to use once motors running, And since you cant use throttle without using AP...stop using throttle. Turn up idle if you want to add air. Cause turning up throttle opening turns up air and gas.
You feel me?
Im; 5 kicks with decomp (I only have manual) find TDC, with decomp, just nudge past tdc, let kicker back up, and zero decomp zero throttle, full choke, idle at least 1/2 turn up from where it was when you last turned off motor.
Like one flick I could see. But no full throttle kicks and no numerous flicks.
45 has been plenty rich for me

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More than about two throttle twists risks flooding the engine.  And if you're in a warm part of Oz, probably one twist is sufficient.  I hold the front brake while kicking to prevent accidentally twisting the throttle.  If you think there's any chance you've flooded it, just automatically do a de-flood drill (hold the throttle continuously wide open, decomp pulled, and kick the engine over a dozen revolutions; you can also push the kill switch if you're superstitious). 

I haven't found it necessary to cycle the engine many revolutions before trying to start it.  Try just the least kicking to find TDC, then go from there.

And try raising the idle speed by half a twist.

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Thanks guys for the suggestions. 

Sorry for the late reply, I've been away from home for some time now.

I played around with the jets and DOT COMs jetting is spot on.

One size bigger pilot (45) and it'll idle with zero turns out on the screw.

I've got a sneaky suspicion that the K&N pod filter might be a little too free flowing for her in the morning. I once accidentally left a rag over the carb inlet with no filter on and it kicked over first try (nearly sucked in the rag too!). As mentioned before, with the old carb it'll kick over first try with the choke. 

Might have to maybe make a sock for the filter when cold starting in winter. I'll continue to experiment with the cold starting. Once warm though, it's a one kick bike.

I'll report back.

Cheers!

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I was amazed at how little fuel squirt is actually needed to keep the engine from stumbling on acceleration. I have an adjustable leak jet on mine and opened it up A LOT. The best way to get an idea of what is going on is to play with the carb when you have it off the bike. I stand in my garage door and shoot gas down the driveway. 

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4 minutes ago, ThumpNRed said:

I stand in my garage door and shoot gas down the driveway. 

I hear BEANO works pretty good.    :lol:

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2 hours ago, JoeRC51 said:

I hear BEANO works pretty good.    :lol:

That would counter what I am trying to achieve! Standing in the driveway... HEAR ME ROAR! 

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On 24/07/2017 at 0:50 AM, notoriousE-R-I-C said:

Is your k+n oiled?

It came oiled but now that I think about it, I doubt it has any oil on it now. I'll check it out in a few days. 

Cheers

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