This is what I know about the 7D Carb.</p>

OS Max had two different manuals for the 7D. The one listed above, for the 7D only, and the 7D-7DV manual. It's in this latter version where you will find more details for the inserts used in this carb, see the attachment.</p>

Next there were actually four different versions of this carb.</p>

The 7DV and three different setups of the 7D carb. The main difference between the 7DV and the 7D was in the carb rotor. The 7DV's rotor had a bore of 8.5mm, while the 7D's rotor bore was 10.5mm without the inserts.</p>

The carb rotor inserts is where the 7D and the 7M shine. When used with a 61FSR or 61VF in the stock configuration the e.g. no pump, the carb required the 8.5mm insert to operate correctly.</p>

For high performance output on the 61FSR and 61VF you could use the 7D with the 9.5mm insert or with no insert (10.5mm bore). The larger openings required the use of a pump for the engine to work correctly. Otherwise the 61FSR or 61VF would have problems drawing fuel at the lower RPMS.</p>

OS Max used the 7D as the stock carb on the 90FSR and the 108FSR as well.</p>

In the case of the 90FSR the I believe the stock configuration was with the 9.5mm insert without pump and of course the utilization of a pump without the rotor insert (10.5mm).</p>

I'm guessing that in the 108FSR the engine would function with (9.5mm) or without (10.5mm) the insert.</p>

One thing I have yet to here is the difference in the perfromance of the 61's using the different configuations.</p>

As a comparison I got out a YS-60FR and Os 61RF-P and measured the throttle bores of each. The YS-60FR had a huge 11.5mm bore and the 61RF-p had a whopping 12mm bore. Of course both these engines had a pump system included.</p>

I suspect that the carb inserts could have left some with a dim view of the 61FSR and 61VF in that using a pump with the 8.5mm insert probably didn't provide the performance boost that they where looking for. Still the YS-60's had a huge throttle bore as compared to OS 61's at that time is probably the main reason for the difference in performance.</p>

Anyone have any performance specs on the different configurations of the 7D?</p>

Bryan.</p>

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