So first let me say…… to the DR FI pioneers….wildwestsydney and msiddalingaiah..... And to Mkane160 for pointing out the fuel injected LT-A700 Suzuki ATV as a possible parts doner.
In setting up the FCR-MX I was dead set against (and proved it in my dyno sheets) that a big bore FCR was not the way to go for the DR650’s torque based powerband. The reason was velocity issues on a larger carb at lower engine speeds. This is an issue with any carb. Too big and your low speed atomization goes to heck in a hand basket. The 39 proved that out when comparing it to the 42mm FCR that I have built up. With FI the fuel is always atomized properly, even better than what a carb can do at any velocity, so there is no performance loss due to unatomized fuel. The second motivation was the dyno sheet after doing the HC piston, Web cam and porting. The slight gain that the 42mm carb showed way up in the over-run RPM on the stock engine now moved to a bigger gain much lower in the powerband and would now actually be useful. So with a larger FI TB I'm expecting better power/torque everywhere.
I’ve received the first piece of the puzzle. A 43mm Suzuki LT-A700 TB. It looks to be just what I need. With its injector already sized very close for the big DR I’m hoping it will eliminate one of the things to figure out in the process. The unit is tiny compared to the FCR-MX so room will not be an issue. It measures 95mm long and has a smaller intake horn, 52mm OD, than the FCR does so making a step-up adapter the correct length to attach the air boot is a no brainer. The intake side is too large for the stock DR intake manifold but not by a large margin. For those of you with an FCR on your bike you know that the FCR was bigger on the manifold side than the BST and is a bit of a challenge to get into the manifold. So going even bigger is not an option. I have a stock LTA manifold coming…. we’ll see how the bolt pattern and port size matches up to the DR’s head.
Isn’t it a beautiful thing? The TB has TPS and IAC on board. It also has a MAP port that is restricted to reduce the MAP signal oscillation that reaches the sensor. I’ve been reading how this is an issue with the manifold pressure pulses of a thumper using the Megasquit’s on board MAP sensor or the standard GM sensor. Since I’m going with a Microsquirt, which does not have on-board MAP, it just seemed logical to me to use the Suzuki LTA remote MAP sensor and even the same hose and length. The big LT-A700 is certainly a thumper. I haven’t tried it yet but I wouldn’t be surprised if the stock DR throttle cable will work as well.
The next issue I’ve been reading about is component electrical connection concerns…. Soldered pin terminals, unsealed connectors…. I just can’t have that on my bike the way I use it. This was also a motivating fact in going with the more costly Microsquirt as it is credit card small and totally weather proof including the plug…… but what about all the connectors on the TB and remote MAP sensor? Ebay to the rescue! I scored the entire wiring harness (cheap) off a LTA700 so I have every sealed connector I need. The additional benefit will be having the LTA700 wiring diagram and wire color codes so I can figure out what did what on the ATV. I’m sure this is going to help in proper connection to the Microsquirt. I have paid keen attention to those that have posted on the FI sites about miss wiring and allowing all the smoke to escape their ECU.
Enough for now...
Edited by mx_rob, 16 December 2009 - 12:28 PM.