MX FCR Project (Monster 750).

[koko64]

What jets you after?

[koko64]

Synched the carbs again.
1. I set the 2 into 1 cables to the same tension so the cams opened in unison.
2. I set the two idle speed knobs by eye to have the cable ends protruding the same amount (1-1.5mm).
3. Then I finished the job with the manometer to get a good setting through the rev range.
4. I had set the two idle mixture screws and slow air jet screws according to the Right Reverend Patrick Burns instructions, with the slides bottomed out.

As you can see, getting one setting wrong can shag the others. A little more complicated than the tandem carb set up.

[Von Eisen]

What jets you after?

Thanks for the "Show and Go" tip, I will give it until the end of this month before I give up hope, if they haven't snailed their way to my door by then I will reorder from that supplier.

Ive ordered Mains 140 ... Pilots 38 and 40 ... I understand these sound a bit small but it seems a characteristic of my motor to prefer weaker jetting, I can only put this down to the porting and manifold matching ? paradoxical as it may seem. Ive tried Mains 145 and Pilots 42, he ran well cold but was way too rich when warmed ... beyond a needle setting.

Your observation on increased torque at lower end is interesting 

Looking forward to your long run update 

[koko64]

Must be good porting= efficiency.

My modified 900 had hi comp pistons, reworked air box, dialed cams, good valve job, very good port work and ported manifolds. I ran 50 pilot jets and could have gone to 48 in FCR 41s if it had a choke.

[koko64]

20200609_213206 by Tony Kokonis, on Flickr

A much easier fit clearing the frame spar with the Niche Cycle boots. Thought I'd fit the K&N velocity stacks for pod filters while I was at it.

However, don't be heavy handed like me. Glad I got spares.

20200609_213104 by Tony Kokonis, on Flickr

[koko64]

Thanks for the "Show and Go" tip, I will give it until the end of this month before I give up hope, if they haven't snailed their way to my door by then I will reorder from that supplier.

Ive ordered Mains 140 ... Pilots 38 and 40 ... I understand these sound a bit small but it seems a characteristic of my motor to prefer weaker jetting, I can only put this down to the porting and manifold matching ? paradoxical as it may seem. Ive tried Mains 145 and Pilots 42, he ran well cold but was way too rich when warmed ... beyond a needle setting.

Your observation on increased torque at lower end is interesting 

Looking forward to your long run update 

I don't have anything that small for FCRs. That's more like Mikuni BDST 38 jetting IME. I wonder what needles, slow air and main air jets are supplied?

[Von Eisen]

I don't have anything that small for FCRs. That's more like Mikuni BDST 38 jetting IME. I wonder what needles, slow air and main air jets are supplied?

Pilots arrived yesterday, still awaiting mains ... Which were sent separately ?  .

Placing a double order on the boots was good foresight ... Fitting well with the filters, I might have to  modify my filters before they fit that well. 

[koko64]

I usually know how it's gonna go .

I drilled out the air jet recesses another 5mm to get enough clearance or else the stacks wouldn't seat on the gasket.  I also skimmed off the lip on each stacks outer bellmouth to slip the filter on without it catching.

[koko64]

The front/horizontal cylinder needed a bigger pilot jet (62) in order to avoid extreme idle mixture screw and SAJ screw settings. The Vert cylinder liked a 60 pilot jet. The IMS and SAJ screws all ended up at 1& 1/2 turns each on both cylinders. I suspect a worn release plate seal in one carb or very asymmetrical manifolds, but someone has shagged the pivot arm screw so the bigger jet is a possible workaround until I can remove it without shagging the very expensive slide. If the seal is ok then it may be a function of very asymmetric intake manifolds. One thing these manifold boots do is exaggerate the difference by a long shot.
Needles raised a notch for a surprisingly major improvement in mid range performance in  both acceleration and smoothness. This bike goes better than I expected so I'm going to check the cams. I'll ask bikeboy if he has dealer records in case DP valves and cams or 900 cams were fitted in its life.

[koko64]

Been getting into the 20's F here. Glad the carbs have chokes.

[koko64]

Did some fine tuning in the idle to 1/4 throttle range (again). Adjusted the idle mixture and idle speed of each carb by ear.  Went totally old school. The bike is the smoothest it's been at low rpms and has the most even idle so far, not easy with the wildly assymmetric manifolds required to fit dirt bike FCRs . I tune carbs regularly for customers with no issue, but these well used carbs have required periodic tuning until they settled down. Despite sonic cleaning and disassembly there are some passages in one carb that have slowly cleared with use. This means the tune has changed with mileage requiring periodic carburettor adjustment. Some jobs require incremental improvement towards perfection while others land bang on target in short order.

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