I suspected a bad EGR Valve in my 87 Suzuki Carry DB71T so I removed it and plugged the intake and exhaust ports where it previously connected. Should this cause any type of performance issues or should it help performance?? I just found and resolved several issues with my carb(choke water lines clogged and jammed fuel cutoff solenoid) now I have a bogging down issue at around 60Km/h in 4th gear if i'm wide open but the bogging goes away if I let off the throttle just a bit. I am suspecting the issue is my carb power valve piston not opening up properly. I have inspected and cleaned all of the components to this power valve, diaphragms are good and all jets are clear. Just wondering if the EGR had some weird connection to this power valve function?
I personally doubt the EGR has anything to do with it given its sole purpose is to re-direct dirty exhaust fumes back into the engine for combustion. If anything, I'll be removing mine permanently. Also I found that odd that it only seems to bog down when you're reaching a certain speed rather than a certain RPM. I would say to maybe try and disconnect the airbox entirely, see if it does it any better. If so, maybe air isn't getting in properly. Otherwise, maybe the floatboal in your carburetor is not adjusted properly? Maybe your vacuum advance is off? Check your vacuum line leading to your distributor. Lastly, maybe check your timing altogether as well if you're equipped to do it.
Thanks for the reply's guys, I have tried all of the above except adjusting the float. I've run it without the air box (actually seemed a little worse...maybe a clue?), hose to vacuum advance is on and working, i've tried setting the timing at 7 thru 15 and it moves clear past the flywheel markings when I rev it, and the fuel filter has been changed. The vacuum holds steady at 15 to 20 when idling and revving a little bit and it idles, and even revs out (under no load) really good. How much vacuum should I be holding while revving fairly high? Maybe I should rig up my vacuum gauge and watch it while it is bogging down? Its only under certain loads, at higher RPM's, and WOT, that it bogs down, if I get past that RPM/load it will recover. And it does bog down a little in other gears as well but most noticeable in 4th at around 60 Km/h. If I ease out of the throttle a little it will then pick up some speed and I can hear the intake sound change and then I can give it full throttle and will eventually get up to 90 Km/h (going down a slight grade). I just feel like that intake sound change is the carb power valve finally opening up (late) and providing that extra needed fuel...? Ive been thinking about cutting a little bit off the spring above the power valve to see if that helps but I dont have another spring in case thats not the problem and I dont want to inject other problems. Maybe there is very small leak in on of the diaphragms that i just cant see? This particular carb does not have a jet needle in the power valve like others I have seen, it simply uncovers a port that is connected to a jet in the bottom of the float bowl...thats a first for me. The fuel flow for the jet in the bottom of the float bowl(the power jet) is controlled by a diaphragm that is vacuum controlled. The diaphragm, when pulled down by vacuum, releases a little ball that then lets fuel flow up through a brass tube, into the throat of the carb, but the power valve has to also move up by vacuum to uncover the jet....very complicated procedure to accomplish a small task and lots of moving parts....balls, diaphragms, ports and vacuum. I will keep digging until I figure it out. I've done it so many times that I can now have this carb out of the truck in less than 2 minutes and same for reinstalling it. lol Thanks again for the suggestions!
Not sure you have a power valve. Most of the carbureted trucks have some form of a constant velocity carb which have a piston Which slides up and down to keep the velocity through the carb high enough to pull fuel out of the main jet. And mine does that full throttle bog under load, at medium rpm, until the choke fully opens.
Jigs, yeah I was calling the piston a power valve, guess the wrong term to use. I have also checked my choke operation and it is fully pegged wide open when warm....i'll keep digging and taking this carb apart...it's probably something simple
Robdjay, did you ever get this fixed? I'm having an identical issue where it bogs down at higher rpm. I have to let the rpms drop a bit before being able to accelerate again. Thanks for your help!
