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Curious if anyone with experience of modding Yamaha 25/30s could help me set the Tohatsu 40 carbs on my 1988 Yamaha 30? The motor came with the carbs installed but I'm not quite sure they were set up right. I don't have any experience with them nor with this motor in factory form so I would appreciate some insight. If someone thinks they may can help let me know and I'll post some pics and go into more detail.
I'll go ahead and share what I know and want to know.
First of all, I know that the motor is a 1988 model Yamaha 30 long shaft. It has even compression in the 130's, and appears stock as far as I can tell aside from the oiler deleted, exhaust holes cut in the mid, the Tohatsu 40 carbs with #122 main jets, and what I believe are Boyesen reeds (yellow ones). It runs fine as is but when I got the motor the throttle linkage where the cam and taming advance mechanism sits was missing one of the 2 bolts and was loose. It also has sat since the fall and the floats are sticking some and fuel is seeping out of all 3 carbs to some degree and the fuel pump has a very very slow drip. I ordered new bowl gaskets, needles and a fuel pump kit but they are yet to be installed. I also have some data from a single test run. I have the motor on a very light and open 1648 Alumacraft flatbottom on a Panther 55 trim unit with 7" of setback. Boat is a 15" transom so I built a static jackplate out of angle and initially installed it level with hull bottom. With just me, the motor ran 30 mph at basically 6000 rpms with a 10" pitch Powertech SRA3 which I believe has been worked to add extra cup and possibly more that a rookie like me can't recognize.
What I don't know includes - are the reed cages factory 30's or the larger ones, has the intake been properly ported to match the carbs, do my carbs have the correct linkages and whatnot, and is the link and sync process for 40 carbs exactly the same as for the factory 30s including pilot air screw adjustments? I do have the factory service manual.
My initial thoughts are that the intake has not been ported which in turn leads me to believe the reed cages are also factory. The linkages and everything looks diff from various pics I have seen so I also question of the carbs are set right either. I'm assuming if the 40's do not have a matching port job then their gains can't be realized and may actually perform worse than the factory carbs. Regarding the on the water performance, I have since raised the motor 1" and will continue to fine tune setup height. I didn't really expect over 30 mph with a 10" prop but I did expect much higher rpms (I did turn off the rev limiter prior to this). Even if the prop has been worked to a higher equivalent pitch I still expected it to turn more. I have a factory SRA3 13 pitch in hand I can now compare against though.
Here are a couple pics of the carb and intake port of the upper carb.
Attachment 74206
https://i.imgur.com/jQ2iLgN.jpg
https://i.imgur.com/ORfVkH5.jpg
those screws holding the butterfly on do not look factory stock
On middle and bottom carbs?Quote:
Originally Posted by hydrospeed77
I reset everything last night so I was actually able to get all 3 butterflies synced up and then I set everything per my factory manual in terms of idle timing, pick-up timing, and static wide open throttle timing, plus idle speed. All mixture screws were about 1.5 turns out so I left them alone. I'm thinking even if this isn't how they are typically set up, this was done correctly at some point but since messed up by someone. The linkage between the top 2 carbs was already spot on so all I had to do was loosen the butterfly screw on the bottom carb, pop it in the linkage and re-tighten. I'm gonna do one more lake test as is and see how it performs plus check actual WOT timing with a light as I changed it pretty drastically as it was statically set to 30 deg. Then going to clean and install the 30 carbs just to compare.
The carbs are a waist of time if you don't work the reeds also. You need 40/50 cages (Yamaha) no stops and CCM reeds. I would also file the extra screw piece sticking through the throttle bar. I do believe 30* is entirely too high.
I recently bought a set of 40/50 cages. They came with the factory SS reeds and a set of CCM reeds. So you would recommend the CCM ones over the Boyesen ones that are currently on mine? My understanding is they will fit both sets of cages.Quote:
Originally Posted by 88workcar
I also got another intake so I can bore one to match the opening on the 40 carbs and keep the other stock to store with my 30 carbs.
My comment on it being set to 30 deg wot may have not been totally accurate. I can't quite remember all of that. I would think if it was set that high I'd remember lol. But it's statically set to 25 degrees now. I'd like to verify with a timing light on the water but it's either been to bright or too rough from me to hang off the back at 30 mph and see haha.
Would you expect the 40 carbs to possibly hurt performance if the intake isn't opened and 40/50 cages used? I just got my 30 carb kit in the mail after about a 3 week wait so I plan to bolt them up freshly cleaned just to see what it does before doing the intake and cages and pairing with the 40 carbs.