Installing/Tuning Mikuni HSR42 on my 1340 EVO - FXR4

[fxr4mikey]

So I finished my build, and part of that was installing the Mikuni HSR42

I didn't remember reading this on the Mikuni site, but they do have a item there that describes that 'some FXR's' MAY have a fitment issue with the control arm ... more on this in a minute.

So I installed it, last part of the build. I didn't notice any fit issue. However the bike wasn't running the best, so with some help from friends, and the good folks here, I determined that the bike was running to lean. So I bought a new idle jet and jet needle. Both one size 'richer' than what comes standard in the carb. The carb comes with a 25 idle jet and a -97 jet neddle, I bought a 27.5 idle jet and a -96 jet needle.

When I took the carb off the bike I thought, DAYUM, I'm lucky it was running good, this would have been a pretty big problem at some time in the future. The top of the carb had been rubbing on the end of the control arm bracket that is welded to the bottom of the back bone. This is the bracket that holds the top hemi joint (control arm) that is bolted to the bracket that is bolted onto the tops of the heads on the left side. Also the vacum port had been rubbing on the head of that bolt that holds the control arm in the bracket, just above the carb.

Here's the pics of this..
you see the damage to the top of the carb, and if you look at the top left of the vac port, you see the damage there too



here's a pic showing the bracket, and wear from the carb. No doubt the carb (being alum) would wear out long before this steel bracket





I was reminded by my Good Friend Harley, that Mikuni talks about this on their website ... so off I went, and here's what they say:

4.Carburetor hits tank or upper motor control arm

There are several possible reasons for this:

1: The manifold is out of position and is pointing "up" toward the tank. This is the most common cause of interference between the Mikuni HSR and the cycle's fuel tank. One clue that this is the case is that the air cleaner bolt holes do not line up with the bolt holes in the heads. Since many air cleaners have some slack in their installation, this is not always a definitive way to check manifold alignment. An angle gauge such as those made for home use can be used to check the alignment of the manifold's mouth.

Use the gauge to compare the angle across the mouth of the intake manifold with the front surface of the points cover or with the seating surfaces of the head breather bolts. The mouth of the carburetor should be parallel with the any of these surfaces.

If the mouth of the manifold is not parallel, loosen the manifold bolts and rotate it until it is.

NOTE: It is a good idea to lubricate the manifold seals as you do this. There is a tendency towards air leaks if the manifold is rotated in the manifold/head seals without some lubrication. WD-40 is convenient and effective. Always check for air leaks after moving the manifold.

2: Some FXR/FLHT frames have the upper lateral control arm mount (this is the folded sheet metal arm that is welded to the frame's backbone just above the carburetor) located slightly low. This can result in interference between the lateral link's mounting bolt and the top of the carburetor. Occasionally, the arm can be so low that it directly hits the top of the HSR Mikuni.

A shorter bolt (Harley fits either of two bolt lengths) or a "button" head bolt mounted with the head down often cures the clearance problem. If it is the arm itself that strikes the top of the carburetor, you may have to consider modifying the arm.



so for me, it was
1) the bracket itself hits the top of the carb
2) the head of the bolt hits the vacuum port

so, I needed to fix it .... I decided to modify the bracket by cutting the back corner of it off to provide clearance for the top of the carb ... here's yur pics
first thing I did was put tape over the intake, and then taped the shop vac hose in place and turned it on. I wanted the shop vac to suck up as much of the cuttings as possible, and didn't want any of it going into the intake. You can't see the shop vac hose, it's just outside the left of the pic, taped up next to the rocker box.





after I cut the piece out, I put the grinding wheel on the dremel and rounded everything over smooth



then I checked the fit ..... sometimes things just don't show in the pics the way they really are ... maybe I didn't have the carb fully seated in the intake, but the fit is 'good' the top of the carb is 'clear' but it's a bit tighter than what shows in this pic




So then I had my new jets installed, and put it back together, warmed it up .... took her out for 15 miles RUNS GREAT !!!!!!!!!!!!!


I still have a problem where that vacuum port hits the head of that bolt on the control arm. I have to take the carb back off, take that vac port off the carb, put some teflon tape on it and put it back in. I need to get it pointed left or down, which will also require a slilghtly longer vacuum line ..... or I can try to find a button head bolt to run thru there. Either way, the carb has to come back off no long rides until that's fixed. It wears a hole in the vacuum line, which operates the VOES and the fuel petcock ........ can't let that loose vacuum ....